Inherent Propensity Research Articles

1H, 15N and 13C assignment of the amyloidogenic protein medin using fast-pulsing NMR techniques.

Thirty-one proteins are known to form extracellular fibrillar amyloid in humans. Molecular information about many of these proteins in their monomeric, intermediate or fibrillar form and how they aggregate and interact to form the insoluble fibrils is sparse. This is because amyloid proteins are notoriously difficult to study in their soluble forms, due to their inherent propensity to aggregate. Using recent developments in fast NMR techniques, band-selective excitation short transient and band-selective optimized flip-angle short-transient heteronuclear multiple quantum coherence we have been able to assign a 5 kDa full-length amyloidogenic protein called medin. Medin is the key protein component of the most common form of localised amyloid with a proposed role in aortic aneurysm and dissection. This assignment will now enable the study of the early interactions that could influence initiation and progression of medin aggregation. The chemical shifts have been deposited in the BioMagRes-Bank accession Nos. 25399 and 26576.

The TWEAK receptor Fn14 is a potential cell surface portal for targeted delivery of glioblastoma therapeutics.

Fibroblast growth factor-inducible 14 (Fn14; TNFRSF12A) is the cell surface receptor for the tumor necrosis factor (TNF) family member TNF-like weak inducer of apoptosis (TWEAK). The Fn14 gene is normally expressed at low levels in healthy tissues but expression is significantly increased after tissue injury and in many solid tumor types, including glioblastoma (GB; formerly referred to as 'GB multiforme'). GB is the most common and aggressive primary malignant brain tumor and the current standard-of-care therapeutic regimen has a relatively small impact on patient survival, primarily because glioma cells have an inherent propensity to invade into normal brain parenchyma, which invariably leads to tumor recurrence and patient death. Despite major, concerted efforts to find new treatments, a new GB therapeutic that improves survival has not been introduced since 2005. In this review article, we summarize studies indicating that (i) Fn14 gene expression is low in normal brain tissue but is upregulated in advanced brain cancers and, in particular, in GB tumors exhibiting the mesenchymal molecular subtype; (ii) Fn14 expression can be detected in glioma cells residing in both the tumor core and invasive rim regions, with the maximal levels found in the invading glioma cells located within normal brain tissue; and (iii) Fn14 engagement as well as Fn14 overexpression can stimulate glioma cell migration, invasion and resistance to chemotherapeutic agents in vitro. We also discuss two new therapeutic platforms that are currently in development that leverage Fn14 overexpression in GB tumors as a way to deliver cytotoxic agents to the glioma cells remaining after surgical resection while sparing normal healthy brain cells.

“Captive to the Demonology of the Iranian Mobs”: U.S. Foreign Policy and Perceptions of Shi’a Islam During the Iranian Revolution, 1978-79

Making use of recently declassified documents, in this article I examine the U.S. government’s perceptions about Shi’a Islam during the time of the Iranian revolution, 1978–9. I show how lower ranking officials in diplomatic and intelligence circles came to the common conception of Shi’ism as being a uniquely populist religion with an inherent propensity towards revolutionary instability, as demonstrated in its doctrines, rituals and history. These perceptions influenced higher levels of government, including President Carter himself. I then explore how analysts and policymakers conceptualized the religious leadership in Iran, especially Khomeini. I show that although opinion was divided about whether Khomeini represented U.S. interests, the prevailing view was to oppose him because of his populist tendencies empowering the Iranian masses, which senior policymakers had come to see as integral to Shi’ism itself. As a result, I argue, although the wider Cold War context dictated the U.S. government’s attempt to maintain diplomatic relations with the new Iranian regime in 1979, this was to be done without overtures to Khomeini, long before the Hostage Crisis.

The effect of factors other than age upon skeletal age indicators in the adult

Context: Estimation of adult age from skeletal remains is problematic due to the weak and variable relationship between age indicators and age.Objectives: To assess the proportion of variation in age indicators that is associated with factors other than age and to attempt to identify what those factors might be.Methods: The paper focuses on frequently used adult bony age markers. A literature search (principally using Web of Science) is conducted to assess the proportion of variation in age indicators associated with factors other than age. The biology of these age markers is discussed, as are factors other than age that might affect their expression.Results: Typically, ∼60% of variation in bony age indicators is associated with factors other than age. Factors including inherent metabolic propensity to form bone in soft tissue, vitamin D status, hormonal and reproductive factors, energy balance, biomechanical variables and genetic factors may be responsible for this variation, but empirical studies are few.Conclusion: Most variation in adult skeletal age markers is due to factors other than age; dry bone study of historic documented skeletal collections and high resolution CT scanning in modern cadavers or living individuals is needed to identify these factors.

Chromatin mediation of a transcriptional memory effect in yeast.

Previous studies have described a transcriptional “memory effect,” whereby transcript levels of many Abf1-regulated genes in the budding yeast Saccharomyces cerevisiae are undiminished even after Abf1 has dissociated from its regulatory sites. Here we provide additional support for this effect and investigate its molecular basis. We show that the effect is observed in a distinct abf1 ts mutant from that used in earlier studies, demonstrating that it is robust, and use chromatin immunoprecipitation to show that Abf1 association is decreased similarly from memory effect and transcriptionally responsive genes at the restrictive temperature. We also demonstrate that the association of TATA-binding protein and Pol II decreases after the loss of Abf1 binding for transcriptionally responsive genes but not for memory effect genes. Examination of genome-wide nucleosome occupancy data reveals that although transcriptionally responsive genes exhibit increased nucleosome occupancy in abf1 ts yeast, the promoter regions of memory effect targets show no change in abf1 ts mutants, maintaining an open chromatin conformation even after Abf1 eviction. This contrasting behavior reflects different inherent propensity for nucleosome formation between the two classes, driven by the presence of A/T-rich sequences upstream of the Abf1 site in memory effect gene promoters. These sequence-based differences show conservation in closely related fungi and also correlate with different gene expression noise, suggesting a physiological basis for greater access to “memory effect” promoter regions. Thus, our results establish a conserved mechanism underlying a transcriptional memory effect whereby sequences surrounding Abf1 binding sequences affect local nucleosome occupancy following loss of Abf1 binding. Furthermore, these findings demonstrate that sequence-based differences in the propensity for nucleosome occupancy can influence the transcriptional response of genes to an altered regulatory signal.

Molecular Basis of Tetramerization and pH-Gating in the KcsA Potassium Channel Cytoplasmic Domain

The intracellular C-terminal domain (CTD) of KcsA, a bacterial homotetrameric potassium channel, is a 40-residue long segment which natively adopts a helical bundle conformation with four-fold symmetry. A hallmark of KcsA behavior is a pH-induced conformational change which leads to opening of the channel at acidic pH. While crystal structures of full-length KcsA failed to observe a pH-effect upon the CTD, other biophysical methods have presented evidence to the contrary. We approached the question of CTD structure and its pH-dependence by studying the behavior of soluble peptides corresponding to residues 128-160 of the CTD (CTD34). A combination of NMR and sedimentation equilibrium experiments established CTD34 to be a tetramer with a KD of (2.0 ± 0.5) x 10−11 M3 at neutral pH, and this tetrameric species undergoes pH-dependent dissociation, rendering CTD34 fully monomeric below pH 5.0. The structural basis for this phenomenon is destabilization of the tetrameric CTD34 by protonation of residue H145 in the monomeric form of the peptide.Molecular factors contributing to CTD tetramerization were investigated by comparing the tetrameric stability of single alanine mutants as determined by NMR, SE and molecular dynamics. Single-residue contributions to tetramer stability were in the 0.5-3.5 kcal/mol range. Hydrophobic interactions between residues lining the tetramer core generally contributed more to formation of tetramer than the inter-subunit salt-bridges between R147 and D149/E152. A third class of residues outside the helical interface influenced tetramer stability via the tetramerization on-rate by changing the inherent helical propensity of CTD34 which promotes tetramer formation. We conclude that the CTD is an independent tetramerization domain modulated by pH, and tetramer formation is controlled by a combination of on- and off-rate effects which conform to current paradigms of protein folding.

Mechanistic Contributions of Biological Cofactors in Islet Amyloid Polypeptide Amyloidogenesis.

Type II diabetes mellitus is associated with the deposition of fibrillar aggregates in pancreatic islets. The major protein component of islet amyloids is the glucomodulatory hormone islet amyloid polypeptide (IAPP). Islet amyloid fibrils are virtually always associated with several biomolecules, including apolipoprotein E, metals, glycosaminoglycans, and various lipids. IAPP amyloidogenesis has been originally perceived as a self-assembly homogeneous process in which the inherent aggregation propensity of the peptide and its local concentration constitute the major driving forces to fibrillization. However, over the last two decades, numerous studies have shown a prominent role of amyloid cofactors in IAPP fibrillogenesis associated with the etiology of type II diabetes. It is increasingly evident that the biochemical microenvironment in which IAPP amyloid formation occurs and the interactions of the polypeptide with various biomolecules not only modulate the rate and extent of aggregation, but could also remodel the amyloidogenesis process as well as the structure, toxicity, and stability of the resulting fibrils.

Spin-Torque and Spin-Hall Nano-Oscillators

This paper reviews the state of the art in spin-torque and spin-Hall-effect-driven nano-oscillators. After a brief introduction to the underlying physics, the authors discuss different implementations of these oscillators, their functional properties in terms of frequency range, output power, phase noise, and modulation rates, and their inherent propensity for mutual synchronization. Finally, the potential for these oscillators in a wide range of applications, from microwave signal sources and detectors to neuromorphic computation elements, is discussed together with the specific electronic circuitry that has so far been designed to harness this potential.

Crystallization of proteins from crude bovine rod outer segments.

Obtaining protein crystals suitable for X-ray diffraction studies comprises the greatest challenge in the determination of protein crystal structures, especially for membrane proteins and protein complexes. Although high purity has been broadly accepted as one of the most significant requirements for protein crystallization, a recent study of the Escherichia coli proteome showed that many proteins have an inherent propensity to crystallize and do not require a highly homogeneous sample (Totir et al., 2012). As exemplified by RPE65 (Kiser, Golczak, Lodowski, Chance, & Palczewski, 2009), there also are cases of mammalian proteins crystallized from less purified samples. To test whether this phenomenon can be applied more broadly to the study of proteins from higher organisms, we investigated the protein crystallization profile of bovine rod outer segment (ROS) crude extracts. Interestingly, multiple protein crystals readily formed from such extracts, some of them diffracting to high resolution that allowed structural determination. A total of seven proteins were crystallized, one of which was a membrane protein. Successful crystallization of proteins from heterogeneous ROS extracts demonstrates that many mammalian proteins also have an intrinsic propensity to crystallize from complex biological mixtures. By providing an alternative approach to heterologous expression to achieve crystallization, this strategy could be useful for proteins and complexes that are difficult to purify or obtain by recombinant techniques.

Bathetic Masochism and the Shrinking Woman

Abstract This essay examines the privileged position given to masochism in some recent critical-theoretical work and argues that a controversy of size is often involved in recalibrations of subjectivity. The masochist is frequently described as a shrinking subject who paradoxically has the potential to function on a grand scale. I track questions of size through certain radical accounts of subjectivity, arguing that such spatial thinking has a complex relation to female subjectivity, which has a long history of being imagined (and stigmatised) as an inherent propensity to smallness and masochistic self-diminution. As a case in point, I address the recent Fifty Shades novels, which romanticise masochism as a shrinking of the female subject accompanied by an increase in her orgasmic and consumer power. The gender-specific implications of shrinking here highlight the potential bathos, or failure, of a radical re-calibration of size effected through masochism. Bathos is seen as an effect of disproportion and I explore the ways in which gendered conventions bathetically 'shrink' female subjects. Finally, I argue that a valorsiation of masochism might reflect the disappointment of certain radical aspirations and demonstrate expansive hopes of transformation shrinking into bathetic adaptation.Key words masochism, size, shrinking, bathos, Bersani, Marx, Fifty Shades of Grey, Berlant[T]he masochist is a revolutionist of self-surrender.Theodor Reik, Masochism in Modern Man (1941)[M]asochism becomes an act of resistance, inseparable from a minority sense of humor.Gilles Deleuze, On Philosophy' in Negotiations, 1972-1990 (1995)I wish to propose that, most significantly, masochism serves life ... What has been repressed from the speculative second half of Freud's text is sexuality as productive masochism. The possibility of exploiting the shattering effects of sexuality in order to maintain the tensions of an eroticized, denarrativized, and mobile consciousness has been neglected, or refused ...Leo Bersani, The Freudian Body (1986)Great claims have recently been made for the power of masochism as a productive mode of resistance. These claims seek to re-imagine masochism as the precursor to radical communal change, rather than positioning it as an individual sexual pathology, and have gained such an aspirational charge that one commentator, remarking on the upsurge in academic interest in masochism at the start of this century, describes it as the 'politically correct form of [postmodern] self-improvement'.1 In this article, I examine the privileging of masochism in some recent critical-theoretical work, and focus on the controversy of size that I believe is at stake in many explorations of radicalized masochism. The radically masochistic subject is often described as a shrinking subject who paradoxically has the potential to function on a grand scale (to produce larger effects - narrative, intersubjective or political; to operate as a model for large-scale change). Questions about the relative size of the subject have long been raised by writers who seek to explore, satirise and critique current configurations of power: these questions of size, I will argue, have a complex relation to radical theories of masochism (a simultaneous shrinking and explosion of the subject), and to female subjectivity, which has a long history of being imagined (and stigmatised) as an inherent propensity to smallness and masochistic self-diminution.An exploration of the radical potential of masochism and its complex relation to questions of size and gender seems particularly apt right now, in the midst of the popularity of the Fifty Shades of Grey series (and forthcoming film), and my approach here is partially a response to the Fifty Shades novels and their deployment of masochism as an aspirational life-style fantasy. This fantasy romanticises masochism as a shrinking of the female subject (smaller, thinner, more child-like), accompanied by an increase in her orgasmic and consumer power (more clothes, more houses, more spectacular climaxes). …

Amyloid Formation by Human Carboxypeptidase D Transthyretin-like Domain under Physiological Conditions

Protein aggregation is linked to a growing list of diseases, but it is also an intrinsic property of polypeptides, because the formation of functional globular proteins comes at the expense of an inherent aggregation propensity. Certain proteins can access aggregation-prone states from native-like conformations without the need to cross the energy barrier for unfolding. This is the case of transthyretin (TTR), a homotetrameric protein whose dissociation into its monomers initiates the aggregation cascade. Domains with structural homology to TTR exist in a number of proteins, including the M14B subfamily carboxypeptidases. We show here that the monomeric transthyretin-like domain of human carboxypeptidase D aggregates under close to physiological conditions into amyloid structures, with the population of folded but aggregation-prone states being controlled by the conformational stability of the domain. We thus confirm that the TTR fold keeps a generic residual aggregation propensity upon folding, resulting from the presence of preformed amyloidogenic β-strands in the native state. These structural elements should serve for functional/structural purposes, because they have not been purged out by evolution, but at the same time they put proteins like carboxypeptidase D at risk of aggregation in biological environments and thus can potentially lead to deposition diseases.

Molecular determinants of tetramerization in the KcsA cytoplasmic domain.

The cytoplasmic C-terminal domain (CTD) of KcsA, a bacterial homotetrameric potassium channel, is an amphiphilic domain that forms a helical bundle with four-fold symmetry mediated by hydrophobic and electrostatic interactions. Previously we have established that a CTD-derived 34-residue peptide associates into a tetramer in a pH-dependent manner (Kamnesky et al., JMB 2012;418:237-247). Here we further investigate the molecular determinants of tetramer formation in the CTD by characterizing the kinetics of monomer-tetramer equilibrium for 10 alanine mutants using NMR, sedimentation equilibrium (SE) and molecular dynamics simulation. NMR and SE concur in finding single-residue contributions to tetramer stability to be in the 0.5 to 3.5 kcal/mol range. Hydrophobic interactions between residues lining the tetramer core generally contributed more to formation of tetramer than electrostatic interactions between residues R147, D149 and E152. In particular, alanine replacement of residue R147, a key contributor to inter-subunit salt bridges, resulted in only a minor effect on tetramer dissociation. Mutations outside of the inter-subunit interface also influenced tetramer stability by affecting the tetramerization on-rate, possibly by changing the inherent helical propensity of the peptide. These findings are interpreted in the context of established paradigms of protein-protein interactions and protein folding, and lay the groundwork for further studies of the CTD in full-length KcsA channels.

Effect of side chain length on intrahelical interactions between carboxylate- and guanidinium-containing amino acids.

The charge-containing hydrophilic functionalities of encoded charged amino acids are linked to the backbone via different numbers of hydrophobic methylenes, despite the apparent electrostatic nature of protein ion pairing interactions. To investigate the effect of side chain length of guanidinium- and carboxylate-containing residues on ion pairing interactions, α-helical peptides containing Zbb-Xaa (i, i+3), (i, i+4) and (i, i+5) (Zbb=carboxylate-containing residues Aad, Glu, Asp in decreasing length; Xaa=guanidinium residues Agh, Arg, Agb, Agp in decreasing length) sequence patterns were studied by circular dichroism spectroscopy (CD). The helicity of Aad- and Glu-containing peptides was similar and mostly pH independent, whereas the helicity of Asp-containing peptides was mostly pH dependent. Furthermore, the Arg-containing peptides consistently exhibited higher helicity compared to the corresponding Agp-, Agb-, and Agh-containing peptides. Side chain conformational analysis by molecular mechanics calculations showed that the Zbb-Xaa (i, i+3) and (i, i+4) interactions mainly involved the χ 1 dihedral combinations (g+, g+) and (g-, g+), respectively. These low energy conformations were also observed in intrahelical Asp-Arg and Glu-Arg salt bridges of natural proteins. Accordingly, Asp and Glu provides variation in helix characteristics associated with Arg, but Aad does not provide features beyond those already delivered by Glu. Importantly, nature may have chosen the side chain length of Arg to support helical conformations through inherent high helix propensity coupled with stabilizing intrahelical ion pairing interactions with the carboxylate-containing residues.

N-Terminal Protein Tails Act as Aggregation Protective Entropic Bristles: The SUMO Case

The formation of β-sheet enriched amyloid fibrils constitutes the hallmark of many diseases but is also an intrinsic property of polypeptide chains in general, because the formation of compact globular proteins comes at the expense of an inherent sequential aggregation propensity. In this context, identification of strategies that enable proteins to remain functional and soluble in the cell has become a central issue in chemical biology. We show here, using human SUMO proteins as a model system, that the recurrent presence of disordered tails flanking globular domains might constitute yet another of these protective strategies. These short, disordered, and highly soluble protein segments would act as intramolecular entropic bristles, reducing the overall protein intrinsic aggregation propensity and favoring thus the attainment and maintenance of functional conformations.

Two-Fold Odd–Even Effect in Self-Assembled Nanowires from Oligopeptide-Polymer-Substituted Perylene Bisimides

Organic nanowires are important building blocks for nanoscopic organic electronic devices. In order to ensure efficient charge transport through such nanowires, it is important to understand in detail the molecular parameters that guide self-assembly of π-conjugated molecules into one-dimensional stacks with optimal constructive π-π overlap. Here, we investigated the subtle relationship between molecular structure and supramolecular arrangement of the chromophores in self-assembled nanowires prepared from perylene bisimides with oligopeptide-polymer side chains. We observed a "two-fold" odd-even effect in circular dichroism spectra of these derivatives, depending on both the number of l-alanine units in the oligopeptide segments and length of the alkylene spacer between chromophore and oligopeptide substituents. Our results indicate that there is a complex interplay between the translation of molecular chirality into supramolecular helicity and the molecules' inherent propensity for well-defined one-dimensional aggregation into β-sheet-like superstructures in the presence of a central chromophore. Strong excitonic coupling as expressed by the appearance of hypsochromically and bathochromically shifted UV-vis absorptions and strong CD signals was systematically observed for molecules with an odd number of l-alanines in the side chains. The latter derivatives gave rise to nanowires with a significantly higher electron mobility. Our results, hence, provide an important design rule for self-assembled organic nanowires.

Tissue-specific aging: a tale of functional asymmetry

Functional asymmetry is a fundamental aspect of all living beings. This also applies to single celled organisms that reproduce symmetrically into two identical halves; the cell that inherits the old pole, it grows at a slower rate, produces less offspring, and shows a decrease in overall cell viability (Stewart EJ et al., PloS Biol 2005; 2:e45). Functional asymmetry becomes clearly visible when one considers the dramatic differences between the immortal germ line and the disposable soma or between the countless cell types of multicellular organisms; most cells differ in their metabolic demands, replicative potential, and developmental origin or are exposed to distinct intrinsic and environmental hazards. However, what makes functional asymmetry more relevant for aging is that any unforeseen cellular mistake will also have asymmetric outcomes for human health e.g. the faulty repair of DNA lesions may have a much higher cost in one direction (e.g. stem cells) than in the other (e.g. hepatocytes). Moreover, functional asymmetry is frequently observed in pathways, such as those involved in more than one biological process; different mutations of the same gene or in different genes of the same pathway could impair one or the other function of that pathway triggering the onset of distinct pathological features. Nucleotide excision repair is a conserved DNA repair pathway that cells employ to recognize and remove helix-distorting DNA lesions (Kamileri et al.; Trends Genet. 2012; 11:566-73). Defects in NER represent some of the best-known examples of functional asymmetry; the clinical outcome of NER patients is exceptionally diverse ranging from increased skin cancer predisposition (as in Xeroderma Pigmentosum) to a wide range of progeroid features (as in Cockayne syndrome or trichothiodystrophy) that once present, they manifest in some, but not all, organs. Recent work from our lab allowed us to gain further insights on how random DNA damage events could trigger the onset of tissue-specific pathological features in NER progeroid syndromes (Karakasilioti I et al. Cell metabolism. 2013; 18:3:403-415). Using mice that lack the NER structure-specific endonuclease ERCC1 systemically or specifically in the adipose tissue, we found that the animals exhibited marked white and brown adipose tissue abnormalities. These appeared to be degenerative changes as both adipose tissue depots developed normally with defects gradually appearing only at later stages in murine life. Further work revealed that the accumulation of irreparable DNA inter-strand crosslinks triggers the transcriptional derepression of pro-inflammatory cytokines in adipocytes, the recruitment of macrophages to sites of tissue damage and the destruction of white adipose tissue depots in NER-defective animals. However, unless one considers the impact of functional asymmetry in age-related diseases, it is rather difficult to appreciate why the adipose tissue would be particularly sensitive to the NER defect. In this respect, a closer look at adipose tissue biology has proven valuable. The oxidation of fats and oils forms radicals capable of crosslinking DNA; in white adipose tissue, where lipids are most abundant, lipid peroxidation would further propagate the formation of irreparable DNA inter-strand crosslinks in ERCC1-defectice adipocytes. Moreover, the adipose tissue itself resembles an ancestral immune organ in many aspects; adipose lineage cells display macrophage properties, adipocytes secrete pro-inflammatory cytokines and the great majority of adipocytes that are located close to lymph nodes are known to interact with lymphoid cells (Caspar-Bauguil Set al., FEBS letters. 2005; 17:3487-3492). Taken together, the NER defect itself, lipid peroxidation and the inherent propensity of adipocytes to activate innate immune responses upon stress could establish self-perpetuating pro-inflammatory cycles. Evidently, the links existing between the adipose tissue and the immune system have evolved to allow injured cells to rapidly communicate their compromised state to the microenvironment; however, the accumulation of irreparable DNA lesions in NER-deficient animals or the gradual wear and tear of adipocytes with aging could establish a chronic inflammatory state leading to adipose tissue degeneration and, in turn, to systemic metabolic dysfunction.

Ground-State Kinetics of Bistable Redox-Active Donor–Acceptor Mechanically Interlocked Molecules

The ability to design and confer control over the kinetics of theprocesses involved in the mechanisms of artificial molecular machines is at the heart of the challenge to create ones that can carry out useful work on their environment, just as Nature is wont to do. As one of the more promising forerunners of prototypical artificial molecular machines, chemists have developed bistable redox-active donor-acceptor mechanically interlocked molecules (MIMs) over the past couple of decades. These bistable MIMs generally come in the form of [2]rotaxanes, molecular compounds that constitute a ring mechanically interlocked around a dumbbell-shaped component, or [2]catenanes, which are composed of two mechanically interlocked rings. As a result of their interlocked nature, bistable MIMs possess the inherent propensity to express controllable intramolecular, large-amplitude, and reversible motions in response to redox stimuli. In this Account, we rationalize the kinetic behavior in the ground state for a large assortment of these types of bistable MIMs, including both rotaxanes and catenanes. These structures have proven useful in a variety of applications ranging from drug delivery to molecular electronic devices. These bistable donor-acceptor MIMs can switch between two different isomeric states. The favored isomer, known as the ground-state co-conformation (GSCC) is in equilibrium with the less favored metastable state co-conformation (MSCC). The forward (kf) and backward (kb) rate constants associated with this ground-state equilibrium are intimately connected to each other through the ground-state distribution constant, KGS. Knowing the rate constants that govern the kinetics and bring about the equilibration between the MSCC and GSCC, allows researchers to understand the operation of these bistable MIMs in a device setting and apply them toward the construction of artificial molecular machines. The three biggest influences on the ground-state rate constants arise from (i) ground-state effects, the energy required to breakup the noncovalent bonding interactions that stabilize either the GSCC or MSCC, (ii) spacer effects, where the structures overcome additional barriers, either steric or electrostatic or both, en route from one co-conformation to the other, and (iii) the physical environment of the bistable MIMs. By managing all three of these effects, chemists can vary these rate constants over many orders of magnitude. We also discuss progress toward achieving mechanostereoselective motion, a key principle in the design and realization of artificial molecular machines capable of doing work at the molecular level, by the strategic implementation of free energy barriers to intramolecular motion.

Distinctive features of the D101N and D101G variants of superoxide dismutase 1; two mutations that produce rapidly progressing motor neuron disease

Mutations in superoxide dismutase 1 (SOD1) associated with familial amyotrophic lateral sclerosis induce misfolding and aggregation of the protein with the inherent propensity of mutant SOD1 to aggregate generally correlating, with a few exceptions, to the duration of illness in patients with the same mutation. One notable exception was the D101N variant, which has been described as wild-type-like. The D101N mutation is associated with rapidly progressing motor neuron degeneration but shows a low propensity to aggregate. By assaying the kinetics of aggregation in a well-characterized cultured cell model, we show that the D101N mutant is slower to initiate aggregation than the D101G mutant. In this cell system of protein over-expression, both mutants were equally less able to acquire Zn than WT SOD1. In addition, both of these mutants were equivalently less able to fold into the trypsin-resistant conformation that characterizes WT SOD1. A second major difference between the two mutants was that the D101N variant more efficiently formed a normal intramolecular disulfide bond. Overall, our findings demonstrate that the D101N and D101G variants exhibit clearly distinctive features, including a different rate of aggregation, and yet both are associated with rapidly progressing disease. We sought to better characterize the biochemical features of two SOD1 mutants associated with rapidly progressing disease, the D101G and wild-type like D101N mutants. We observed using our cell model that that although similarities were observed when comparing the ability to bind metals and resist trypsin digestion, these mutants differed in their ability to initiate aggregation and to form the normal intramolecular disulfide bond. We conclude that these mutants exhibit distinct properties despite producing similar disease phenotypes in patients.

An assessment of the intercarbon stretching phenomenon in C-substituted “pseudocloso” {3,1,2-RuC2B9} metalladicarbaboranes

DFT calculation of cluster shapes and their related boron-vertex 11B nuclear shieldings for a range of substituted 12-vertex metalladicarbaborane cluster compounds [3,1,2-R2-3-(η6-C6H6)-3,1,2-RuC2H9H9] confirms that the array of experimentally observed C–C distances in the group of progressively more open closo, ‘semipseudocloso’ and ‘pseudocloso’ clusters results from the inherent propensity of the [(η6-C6H6)RuC2H9H9R2] cluster to occupy, in the absence of steric drivers, either closo-structured or so-called ‘pseudocloso’-structured fundamental local minima on the overall potential energy surface. The shallow profiles of the potential wells, together with the electronic and steric influences of substituents on the cluster carbon vertices, alter the relative energies of the closo and ‘pseudocloso’ minima, and alter the energy profile between them, thereby accounting for the observed variations in the distances in the crystallographically measured C–C separations. We propose that these differ fundamentally due to either the closo or ‘pseudocloso’ configuration being electronically preferred, with some instances of the ‘pseudocloso’ configuration being compressed towards closo by packing forces, or stretched further beyond ‘pseudocloso’ by steric effects of bulky substituents on carbon. This contrasts with one view postulated in the literature which holds that steric repulsion between the C-bound substituents is the sole driver that forces an inherently fundamental closo cluster to open into an anomalous ‘pseudocloso’ configuration. In two reported cases, the cluster flexibility is evident in solution and, in these cases, GIAO calculation of the 11B chemical shieldings explains the measured 11B chemical shifts, which can be interpreted in terms of the dynamic interchange of the closo and ‘pseudocloso’ species. A currently held view is that the ‘weighted average’ of 11B chemical shifts reflects the inherent degree of electronic ‘pseudocloso’ character in a particular cluster can therefore often equally be rationalised in terms of lability between similarly stable fundamentally closo and ‘pseudocloso’ forms.

Fetal growth restriction promotes physical inactivity and obesity in female mice

BackgroundEnvironmental exposures during critical periods of prenatal and early postnatal life affect the development of mammalian body weight regulatory mechanisms, influencing lifelong risk of obesity. The specific biologic processes that mediate the persistence of such effects, however, remain poorly understood.ObjectiveThe objectives were to determine the developmental timing and physiological basis of the obesity-promoting effect previously reported in offspring of obese agouti viable yellow (Avy/a) mothers.DesignNewborn offspring of obese agouti viable yellow (Avy/a) and lean (a/a) mothers were cross-fostered shortly after birth to study separately the effects of in utero or suckling-period exposure to Avy/a dams. Body composition, food intake, physical activity, and energy expenditure were measured in offspring shortly after weaning and in adulthood.ResultsOffspring of obese Avy/a dams paradoxically experienced fetal growth restriction, which was followed by adult-onset obesity specifically in females. Our main analyses focused on wild type (a/a) offspring, because a subset of adult Avy/a offspring contracted a kidney disease resembling diabetic nephropathy. Detailed physiological characterization demonstrated that, both shortly after weaning and in adulthood, female wild type mice born to Avy/a mothers are not hyperphagic, but have reduced physical activity and energy expenditure. No such coordinated changes were detected in male offspring. Mediational regression analysis of our longitudinal data supported a causal pathway in which fetal growth restriction persistently reduces physical activity, leading to adult obesity.ConclusionsOur data are consistent with several recent human epidemiologic studies showing female-specific effects of perinatal nutritional restriction on later obesity, and provide the novel mechanistic insight that this may occur via permanent and sex-specific changes in one’s inherent propensity for physical activity.