Oligomerization Activity Research Articles

A Subsidiary Cell-Localized Glucose Transporter Promotes Stomatal Conductance and Photosynthesis.

It has long been recognized that stomatal movement modulates CO2 availability and as a consequence the photosynthetic rate of plants, and that this process is feedback-regulated by photoassimilates. However, the genetic components and mechanisms underlying this regulatory loop remain poorly understood, especially in monocot crop species. Here, we report the cloning and functional characterization of a maize (Zea mays) mutant named closed stomata1 (cst1). Map-based cloning of cst1 followed by confirmation with the clustered regularly interspaced short palindromic repeats (CRISPR)/ CRISPR associated protein 9 system identified the causal mutation in a Clade I Sugars Will Eventually be Exported Transporters (SWEET) family gene, which leads to the E81K mutation in the CST1 protein. CST1 encodes a functional glucose transporter expressed in subsidiary cells, and the E81K mutation strongly impairs the oligomerization and glucose transporter activity of CST1. Mutation of CST1 results in reduced stomatal opening, carbon starvation, and early senescence in leaves, suggesting that CST1 functions as a positive regulator of stomatal opening. Moreover, CST1 expression is induced by carbon starvation and suppressed by photoassimilate accumulation. Our study thus defines CST1 as a missing link in the feedback-regulation of stomatal movement and photosynthesis by photoassimilates in maize.

The effect of phenolic compounds on salicylaldimine nickel-catalyzed ethylene oligomerization

A salen nickel complex has been prepared in good yield with ethylenediamine, salicylaldehyde, and NiCl2·6H2O as raw materials. The structure of the complex was characterized by FTIR, 1H NMR, UV, and ESI-MS. Upon activation with methylaluminoxane (MAO), the precatalyst showed high activity for ethylene oligomerization. To reduce the simultaneous production of insoluble polymers during the nickel-catalyzed ethylene oligomerization, a series of phenolic compounds were introduced as modifiers for the production of linear α-olefins. The researched result showed that the phenolic compounds have a significant impact on the selectivity of oligomers and the concentration of polymers. With the increase of phenolic compounds, the content of polymers decreased and the distribution of oligomers gradually shifted toward lighter olefins. The sterically hindered 4-tert-butyphenol proved to be an especially efficient polymer-retarding modifier among the studied phenolic compounds in this work. Furthermore, the retarding effect of phenolic compounds toward insoluble polymers may be mainly related to their interaction with MAO, giving rise to larger MAO aggregates.

Covalently Linking Oligomerization-Impaired GlpF Protomers Does Not Completely Re-establish Wild-Type Channel Activity.

Integral membrane proteins of the aquaporin family facilitate rapid water flux across cellular membranes in all domains of life. Although the water-conducting pore is clearly defined in an aquaporin monomer, all aquaporins assemble into stable tetramers. In order to investigate the role of protomer–protomer interactions, we analyzed the activity of heterotetramers containing increasing fractions of mutated monomers, which have an impaired oligomerization propensity and activity. In order to enforce interaction between the protomers, we designed and analyzed a genetically fused homotetramer of GlpF, the aquaglyceroporin of the bacterium Escherichia coli (E. coli). However, increasing fractions of the oligomerization-impaired mutant GlpF E43A affected the activity of the GlpF heterotetramer in a nearly linear manner, indicating that the reduced protein activity, caused by the introduced mutations, cannot be fully compensated by simply covalently linking the monomers. Taken together, the results underline the importance of exactly positioned monomer–monomer contacts in an assembled GlpF tetramer.

Long noncoding RNA NEXN-AS1 mitigates atherosclerosis by regulating the actin-binding protein NEXN.

Noncoding RNAs are emerging as important players in gene regulation and disease pathogeneses. Here, we show that a previously uncharacterized long noncoding RNA, nexilin F-actin binding protein antisense RNA 1 (NEXN-AS1), modulates the expression of the actin-binding protein NEXN and that NEXN exerts a protective role against atherosclerosis. An expression microarray analysis showed that the expression of both NEXN-AS1 and NEXN was reduced in human atherosclerotic plaques. In vitro experiments revealed that NEXN-AS1 interacted with the chromatin remodeler BAZ1A and the 5' flanking region of the NEXN gene and that it also upregulated NEXN expression. Augmentation of NEXN-AS1 expression inhibited TLR4 oligomerization and NF-κB activity, downregulated the expression of adhesion molecules and inflammatory cytokines by endothelial cells, and suppressed monocyte adhesion to endothelial cells. These inhibitory effects of NEXN-AS1 were abolished by knockdown of NEXN. In vivo experiments using ApoE-knockout mice fed a Western high-fat diet demonstrated that NEXN deficiency promoted atherosclerosis and increased macrophage abundance in atherosclerotic lesions, with heightened expression of adhesion molecules and inflammatory cytokines, whereas augmented NEXN expression deterred atherosclerosis. Patients with coronary artery disease were found to have lower blood NEXN levels than healthy individuals. These results indicate that NEXN-AS1 and NEXN represent potential therapeutic targets in atherosclerosis-related diseases.

The quaternary structure of human tyrosine hydroxylase: effects of dystonia-associated missense variants on oligomeric state and enzyme activity.

Tyrosine hydroxylase (TH) is a multi‐domain, homo‐oligomeric enzyme that catalyses the rate‐limiting step of catecholamine neurotransmitter biosynthesis. Missense variants of human TH are associated with a recessive neurometabolic disease with low levels of brain dopamine and noradrenaline, resulting in a variable clinical picture, from progressive brain encephalopathy to adolescent onset DOPA‐responsive dystonia (DRD). We expressed isoform 1 of human TH (hTH1) and its dystonia‐associated missense variants in E. coli, analysed their quaternary structure and thermal stability using size‐exclusion chromatography, circular dichroism, multi‐angle light scattering, transmission electron microscopy, small‐angle X‐ray scattering and assayed hydroxylase activity. Wild‐type (WT) hTH1 was a mixture of enzymatically stable tetramers (85.6%) and octamers (14.4%), with little interconversion between these species. We also observed small amounts of higher order assemblies of long chains of enzyme by transmission electron microscopy. To investigate the role of molecular assemblies in the pathogenesis of DRD, we compared the structure of WT hTH1 with the DRD‐associated variants R410P and D467G that are found in vicinity of the predicted subunit interfaces. In contrast to WT hTH1, R410P and D467G were mixtures of tetrameric and dimeric species. Inspection of the available structures revealed that Arg‐410 and Asp‐467 are important for maintaining the stability and oligomeric structure of TH. Disruption of the normal quaternary enzyme structure by missense variants is a new molecular mechanism that may explain the loss of TH enzymatic activity in DRD. Unstable missense variants could be targets for pharmacological intervention in DRD, aimed to re‐establish the normal oligomeric state of TH.

A Series of Novel Dendritic Salicylaldimine Iron Catalysts: Synthesis, Characterization, and Application in Ethylene Oligomerization

A series of novel dendritic salicylaldimine ligands and their corresponding iron complexes have been synthesized using 1.0 generation (1.0 G) dendritic macromolecules, salicylaldehyde and FeCl2 · 4H2O as raw materials. The structures of the ligands and iron complexes were characterized by FT-IR, 1H NMR, UV, ESI-MS, and elemental analysis. The dendritic salicylaldimine iron complexes presented moderate catalytic activity in ethylene oligomerization and selectivity for higher carbon number olefins products (≥C8) when they were activated with methylaluminoxane (MAO). The catalytic activity and product selectivity were related to the co-catalyst, solvent, bridged group length and reaction parameters such as reaction temperature, Al/Fe molar ratio and ethylene pressure. The complex C3 showed the highest catalytic activity (up to 13.75 × 104 g (mol Fe h)–1) and the selectivity of higher carbon number olefins (35.31%) at the optimized conditions. Moreover, the catalytic properties of dendritic salicylaldimine iron complex C3 was better than non-dendritic iron complex.

TAK-243, a Small Molecule Inhibitor of Ubiquitin-Activating Enzyme (UAE), Induces ER Stress and Apoptosis in CLL Cells

Introduction: Despite the promise of B-cell receptor-associated kinase inhibitors (BCRi) in CLL, resistance to these agents is inevitable. Ubiquitin-proteasome systems are altered in cancer, leading to destabilization of tumor suppressors, overexpression of proto-oncogenes (e.g., MYC), and impaired DNA repair. Neoplastic B cells exhibit a state of heightened cellular stress and are thereby susceptible to endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). The UPR is activated in CLL cells upon sIgM signaling and inhibited by ibrutinib. Proteasome inhibitors demonstrate clinical activity in certain types of B-cell neoplasia but are inactive in CLL. Here, we investigated an alternative approach to harness the pro-apoptotic UPR in CLL by using TAK-243, a first-in-class small molecule UAE inhibitor.Methods: Peripheral blood cells were obtained from patients with CLL (N=20) and isolated using Ficoll-Hypaque techniques. TAK-243 was obtained from Millennium Pharmaceuticals, Inc., a wholly owned subsidiary of Takeda Pharmaceutical Company Limited (Cambridge, MA). TAK-243 efficacy was assessed in CLL cells and 10 DLBCL (diffuse large B-cell lymphoma) cell lines.Results: TAK-243 induced ER stress and the UPR in CLL cells, followed by rapid apoptosis within 2 hours. Following 24-hour incubation, we established an IC50 of ~50 nM (Annexin V+ cells) in CLL cells. By contrast, primary B cells and T cells were less sensitive to TAK-243. Given the importance of tumor microenvironment in CLL cell survival, we evaluated the effect of TAK-243 in a CD40L-expressing stromal co-culture model. Whereas CD40L-stimulated CLL cells were resistant to BCRi, they were fully sensitive to UAE inhibition. TAK-243 had a similar IC50 (~50 nM) across DLBCL cell lines, independent of cell of origin.Treatment with TAK-243 rapidly disrupted ubiquitin conjugation and degradation of proteins controlled by the UPS in CLL cells and DLBCL cell lines. UPR induction occurred within 2 hours, as shown by activation of eIF2α (in both CLL and DLBCL cells) and oligomerization and autophosphorylation of PERK (in DLBCL cells). After 4 hours, neoplastic B cells exhibited late apoptotic phase of the UPR: transcriptional induction of CHOP, GADD34, and NOXA. These events were accompanied by upregulation of pro-apoptotic BH3-only proteins, stabilization of Mcl-1 and, ultimately, cleavage of caspase-3 and PARP. TAK-243 inhibited NFκB pathway, as shown by accumulation of IκBα, a negative pathway regulator. The extent of the UPR in CLL cells varies depending on the initiating signal. For example, B-cell receptor crosslinking induced expression of CHOP and GRP78 in CLL cells, but only weak activation of PERK and no IRE1-dependent processing of XBP1 (Krysov S, et al. Blood. 2014). Targeting UAE in CLL cells induced robust activation of eIF2α, upregulation of CHOP, GADD34 as well as NOXA mRNA, indicating high sensitivity to this pathway.TAK-243 induced a more rapid UPR and exhibited lower IC50 compared with the proteasome inhibitor bortezomib in CLL and DLBCL cells. While both drugs induced autophagy as shown by LC3 processing, only bortezomib treatment led to p62 degradation, suggesting that autophagy was inefficient in response to TAK-243 due to lack of ubiquitin conjugation. Our findings were confirmed in a mouse lymphoma xenograft model. OCI-LY3 cells were inoculated subcutaneously in the right flank of NSG mice and treatment with TAK-243 (10 or 20 mg/kg IV twice weekly) or vehicle control began when tumors reached 10 mm in size. Treatment led to reduced tumor progression, induction of ER stress, and decreased cell proliferation and survival.Conclusions: The UAE inhibitor TAK-243 induces ER stress and promotes apoptosis in CLL cells in vitro and restricts lymphoma growth in vivo. TAK-243 exhibited greater in-vitro cytotoxicity in lymphoma cells compared to bortezomib. Targeting UAE is a novel approach to disrupt the UPS which may hold promise in therapy of CLL and other B-cell malignancies. DisclosuresSpurgeon:Bristol Myers Squibb: Research Funding; Gilead Sciences, Inc.: Consultancy, Research Funding; Oncternal: Research Funding; Acerta: Research Funding; Genentech: Research Funding; Janssen: Research Funding; Pharmacyclics: Consultancy, Research Funding; MEI Pharma: Consultancy. Berger:Takeda Pharmaceuticals International Co.: Employment. Danilov:TG Therapeutics: Consultancy; Aptose Biosciences: Research Funding; Astra Zeneca: Consultancy; Genentech: Consultancy, Research Funding; Bayer Oncology: Consultancy, Research Funding; Verastem: Consultancy, Research Funding; Gilead Sciences: Consultancy, Research Funding; Takeda Oncology: Research Funding.

The cristae modulator Optic atrophy 1 requires mitochondrial ATP synthase oligomers to safeguard mitochondrial function

It is unclear how the mitochondrial fusion protein Optic atrophy 1 (OPA1), which inhibits cristae remodeling, protects from mitochondrial dysfunction. Here we identify the mitochondrial F1Fo-ATP synthase as the effector of OPA1 in mitochondrial protection. In OPA1 overexpressing cells, the loss of proton electrochemical gradient caused by respiratory chain complex III inhibition is blunted and this protection is abolished by the ATP synthase inhibitor oligomycin. Mechanistically, OPA1 and ATP synthase can interact, but recombinant OPA1 fails to promote oligomerization of purified ATP synthase reconstituted in liposomes, suggesting that OPA1 favors ATP synthase oligomerization and reversal activity by modulating cristae shape. When ATP synthase oligomers are genetically destabilized by silencing the key dimerization subunit e, OPA1 is no longer able to preserve mitochondrial function and cell viability upon complex III inhibition. Thus, OPA1 protects mitochondria from respiratory chain inhibition by stabilizing cristae shape and favoring ATP synthase oligomerization.

Geometric isomerism effect on catalytic activities of bis(oxalato)diaquochromates(III) for 2-chloroallyl alcohol oligomerization

Abstract The cis- and trans-potassium bis(oxalato)diaquochromates(III) have been studied towards their catalytic activity for the 2-chloroallyl alcohol oligomerization. The geometric isomerism effect on the oligomerization products under mild reaction conditions has been investigated. The molecular masses and tactic structures of obtained poly(2-chloroallyl alcohols) have been compared and analyzed. The mechanisms of oligomerization processes have been proposed. It has been proven that two studied complexes – cis-\(\hbox {K}[\hbox {Cr}(\hbox {C}_{2}\hbox {O}_{4})_{2}(\hbox {OH}_{2})_{2}]\) and trans-\(\hbox {K}[\hbox {Cr}(\hbox {C}_{2}\hbox {O}_{4})_{2}(\hbox {OH}_{2})_{2}]\cdot \hbox {3H}_{2}\hbox {O}\) are highly active catalysts for the oligomerization of the beta-olefin derivative. Graphical Abstract SYNOPSIS: The investigations show the catalytic activity of cis- and trans-potassium bis(oxalato)diaquochromates(III) for the 2-chloroallyl alcohol oligomerization. The geometric isomerism effect in the bis(oxalato)diaquochromates(III) has been analyzed for the values of the catalytic activity of the synthesized complexes and the identity of the oligomerization products.

Replacing the 238th aspartic acid with an arginine impaired the oligomerization activity and inflammation-inducing property of pyolysin

ABSTRACT Trueperella pyogenes (T. pyogenes) is an important opportunistic pathogen. Pyolysin (PLO) importantly contributes to the pathogenicity of T. pyogenes. However, the relationship between the structure and function and the virulence of PLO is not well documented. In the current study, recombinant PLO (rPLO) and three rPLO mutants were prepared. rPLO D238R, a mutant with the 238th aspartic acid replaced with an arginine, showed impairment in oligomerization activity on cholesterol-containing liposome and pore-forming activity on sheep red blood cell membrane. Further study employing the prepared mutants confirmed that the pore-forming activity of PLO is essential for inducing excessive inflammation responses in mice by upregulating the expression levels of IL-1β, TNF-α, and IL-6. By contrast, rPLO P499F, another mutant with impaired cell membrane binding capacity, elicited an inflammation response that was dependent on pathogen-associated molecular pattern (PAMP) activity, given that the mutant significantly upregulated the expression of IL-10 in macrophages and in mice, whereas rPLO did not. Results indicated that domain 1 of the PLO molecule plays an important role in maintaining pore-forming activity. Moreover, the PLO pore-forming activity and not PAMP activity is responsible for the inflammation-inducing effect of PLO. The results of this study provided new information for research field on the structure, function, and virulence of PLO. Abbreviations: T. pyogenes: Trueperella pyogenes; PLO: Pyolysin; rPLO: recombinant PLO; PAMP: pathogen-associated molecular pattern; CDCs: cholesterol-dependent cytolysins; PLY: pneumolysin; NLRP3: NLR family pyrin domain containing protein 3; PRRs: pattern recognition receptors; Asp: aspartic acid; TLR4: Toll-like receptor 4; Arg: arginine; Asn: asparagine; IPTG: Isopropyl-β-d-thiogalactoside; PBS: phosphate-buffered saline; sRBCs: sheep red blood cells; TEM: Transmission electron microscopy; RBCM: red blood cell membrane; SDS-PAGE: sodium dodecyl sulfate–polyacrylamide gel electrophoresis; NC membrane: nitrocellulose membrane; SDS-AGE: dodecyl sulfate agarose gel electrophoresis; MDBK cells: Madin–Darby bovine kidney cells; RPMI-1640 medium: Roswell Park Memorial Institute-1640 medium; FBS: fetal bovine serum; BMDMs: bone marrow-derived macrophages; TNF-α: tumor necrosis factor α; IL-1β: interleukin-1β; IFN-γ: interferon-γ; TGF-β: transforming growth factor-β; ELISA: enzyme-linked immunosorbent assay

Molecular basis for the loss-of-function effects of the Alzheimer's disease–associated R47H variant of the immune receptor TREM2

Triggering receptor expressed on myeloid cells 2 (TREM2) is an immune receptor expressed on the surface of microglia, macrophages, dendritic cells, and osteoclasts. The R47H TREM2 variant is a significant risk factor for late-onset Alzheimer's disease (AD), and the molecular basis of R47H TREM2 loss of function is an emerging area of TREM2 biology. Here, we report three high-resolution structures of the extracellular ligand-binding domains (ECDs) of R47H TREM2, apo-WT, and phosphatidylserine (PS)-bound WT TREM2 at 1.8, 2.2, and 2.2 Å, respectively. The structures reveal that Arg47 plays a critical role in maintaining the structural features of the complementarity-determining region 2 (CDR2) loop and the putative positive ligand-interacting surface (PLIS), stabilizing conformations capable of ligand interaction. This is exemplified in the PS-bound structure, in which the CDR2 loop and PLIS drive critical interactions with PS via surfaces that are disrupted in the variant. Together with in vitro and in vivo characterization, our structural findings elucidate the molecular mechanism underlying loss of ligand binding, putative oligomerization, and functional activity of R47H TREM2. They also help unravel how decreased in vitro and in vivo stability of TREM2 contribute to loss of function in disease.

Synthesis of low-molecular-weight poly-α-olefins using silicon-bridged zirconocene catalyst for lubricant basestock

The oily oligomers with low-molecular-weight, medium kinematic viscosity and high viscosity index are yielded through oligomerizations of higher α-olefins (1-hexene, 1-octene, 1-decene, 1-dodecene and 1-tetradecene) and co-oligomerization of 1-decene with 1-butene in the presence of the silicon-bridged Ph2Si(Cp)(9-Flu)ZrCl2 catalyst and the methylaluminoxane co-catalyst. The oligomerization activity is affected by the bulkiness and lateral size of monomer, and the viscosity of oligomer obtained. Through adding of 1-butene to 1-decene, the oligomerization activity is decreased, but viscosity index of oligomer obviously is increased. The highest co-oligomerization activity of 1-decene with 1-butene is presented at the temperature of 60 °C and Al/Zr molar ratio of 300. 1H and 13C NMR spectroscopy reveal that four types of vinylidene are existed in oligomers and the major olefinic bonds are internal disubstituted vinylidene, which are produced through 2,1-misinsertion and β-hydride elimination, or 2,1-misinsertion and rearrangement followed by β-hydride elimination. The chain termination of oligomerization of α-olefins favors chain transfer to the co-catalyst to produce saturated end group. The oligomerization pathways are summarized.

Plasmodium falciparum RUVBL3 protein: a novel DNA modifying enzyme and an interacting partner of essential HAT protein MYST

RUVBLs constitute a conserved group of ATPase proteins that play significant role in a variety of cellular processes including transcriptional regulation, cell cycle and DNA damage repair. Three RUVBL homologues, namely, PfRUVBL1, PfRUVBL2 and PfRUVBL3 have been identified in P. falciparum, unlike its eukaryotic counterparts, which have two RUVBL proteins (RUVBL1 & RUVBL2). The present study expands our understanding of PfRUVBL3 protein and thereby basic biology of Plasmodium in general. Here, we have shown that parasite PfRUVBL3 is a true homolog of human/yeast RUVBL2 protein. Our result show that PfRUVBL3 constitutively expresses throughout the stages of intra-erythrocytic cycle (IDC) with varied localization. In addition to ATPase and oligomerization activity, we have for the first time shown that PfRUVBL3 possess DNA cleavage activity which interestingly is dependent on its insertion domain. Furthermore, we have also identified RUVBL3 to be an interacting partner of an essential chromatin remodeling protein PfMYST and together they colocalize with H3K9me1 histone in parasitophorous vacuole during the ring stage of IDC suggesting their potential involvement in chromatin remodeling and gene transcription.

NMR chemical shift analysis decodes olefin oligo- and polymerization activity of d0 group 4 metal complexes

d0 metal-alkyl complexes (M = Ti, Zr, and Hf) show specific activity and selectivity in olefin polymerization and oligomerization depending on their ligand set and charge. Here, we show by a combined experimental and computational study that the 13C NMR chemical shift tensors of the α-carbon of metal alkyls that undergo olefin insertion signal the presence of partial alkylidene character in the metal-carbon bond, which facilitates this reaction. The alkylidene character is traced back to the π-donating interaction of a filled orbital on the alkyl group with an empty low-lying metal d-orbital of appropriate symmetry. This molecular orbital picture establishes a connection between olefin insertion into a metal-alkyl bond and olefin metathesis and a close link between the Cossee-Arlmann and Green-Rooney polymerization mechanisms. The 13C NMR chemical shifts, the α-H agostic interaction, and the low activation barrier of ethylene insertion are, therefore, the results of the same orbital interactions, thus establishing chemical shift tensors as a descriptor for olefin insertion.

Preparation of Aryloxy-aluminoxanes and Their Use as Activators in the Bis(imino)pyridyl Iron-catalyzed Oligomerization of Ethylene

In this study, a series of aryloxy-aluminoxanes originated directly from the hydrolysis of reaction products of AlMe3 and phenols were synthesized, which could serve as effective polymer-retarding activators for the iron-catalyzed ethylene oligomerization. The molar ratios of [PhOH]/[AlMe3] and [H2O]/[Al] during the preparation were explored and their impacts on the oligomerization activity and product distribution were discussed. To obtain the effective activators with good polymer-retarding effect and relatively high activity, the optimized conditions were proposed to be [PhOH]/[AlMe3] = 0.5 and [H2O]/[Al] = 0.7. Various aluminoxanes with different [―OH] sources confirmed the importance of using phenols in preparing the effective polymer-retarding activators. By utilizing these aryloxy-aluminoxanes, the mass fraction of polymers in the total products could be reduced to lower than 1.0 wt%, which is much lower than that of the MAO-activated systems (> 30 wt%). This is a potential benefit for the industrial application of the iron-catalyzed oligomerization process.

Fluorescence-based approaches for monitoring membrane receptor oligomerization

Membrane protein structures are highly under-represented relative to water-soluble protein structures in the protein databank. This is especially the case because membrane proteins represent more than 30% of proteins encoded in the human genome yet contribute to less than 10% of currently known structures (Torres et al. in Trends Biol Sci 28:137-144, 2003). Obtaining high-resolution structures of membrane proteins by traditional methods such as NMR and x-ray crystallography is challenging, because membrane proteins are difficult to solubilise, purify and crystallize. Consequently, development of methods to examine protein structure in situ is highly desirable. Fluorescence is highly sensitive to protein structure and dynamics (Lakowicz in Principles of fluorescence spectroscopy, Springer, New York, 2007). This is mainly because of the time a fluorescence probe molecule spends in the excited state. Judicious choice and placement of fluorescent molecule(s) within a protein(s) enables the experimentalist to obtain information at a specific site(s) in the protein (complex) of interest. Moreover, the inherent multi-dimensional nature of fluorescence signals across wavelength, orientation, space and time enables the design of experiments that give direct information on protein structure and dynamics in a biological setting. The purpose of this review is to introduce the reader to approaches to determine oligomeric state or quaternary structure at the cell membrane surface with the ultimate goal of linking the oligomeric state to the biological function. In the first section, we present a brief overview of available methods for determining oligomeric state and compare their advantages and disadvantages. In the second section, we highlight some of the methods developed in our laboratory to address contemporary questions in membrane protein oligomerization. In the third section, we outline our approach to determine the link between protein oligomerization and biological activity.

Application of Modified Clay Catalysts in Oligomerization of Light Olefins

The oligomerization of light olefins to high-octane clean engine fuels is one possible way to solve increased requirements for motor fuels. This paper presents a study of catalytic oligomerization of C 2 -C 4 olefins on Ru-Fe supported pillared clay catalyst with different metallic quantity. The prepared catalysts were characterized by X-ray diffraction, N 2 adsorption-desorption at 77K, BET and BJH methods. The BET and BJH methods showed the pillared clay had significantly increased surface area and when an appropriate amount of Ru and Fe were added, the bimetallic alloys were uniformly dispersed on the modified clay surfaces and had an average mesopore size of 4.1 nm. It is indicated that excess metal oxides blocked the surface of bimetallic RuFe/MMC system, resulted in decreased catalytic activity. The low metal content catalysts showed higher oligomerization activity and increasing the Fe content gave selectivity to isomerization reactions.

Frontline Science: Specialized proresolving lipid mediators inhibit the priming and activation of the macrophage NLRP3 inflammasome.

The prototypic proinflammatory cytokine IL-1β plays a central role in innate immunity and inflammatory disorders. The formation of mature IL-1β from an inactive pro-IL-1β precursor is produced via nonconventional multiprotein complexes called the inflammasomes, of which the most common is the nucleotide-binding domain leucine-rich repeat-containing protein 3 (NLRP3) inflammasome composed by NLRP3, (ASC) apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (CARD), and caspase-1. Specialized proresolving mediators (SPMs) promote resolution of inflammation, which is an essential process to maintain host health. SPMs prevent excessive inflammation by terminating the inflammatory response and returning to tissue homeostasis without immunosupression. This study tested the hypothesis that modulation of the NLRP3 inflammasome in macrophages is one mechanism involved in the SPM-regulated processes during resolution. Our findings demonstrate that the SPM resolvin D2 (RvD2) suppressed the expression of pro-IL-1β and reduced the secretion of mature IL-1β in bone marrow-derived macrophages challenged with LPS+ATP (classical NLRP3 inflammasome model) or LPS+palmitate (lipotoxic model). Similar findings were observed in thioglycolate-elicited peritoneal macrophages, in which RvD2 remarkably reduced ASC oligomerization, inflammasome assembly, and caspase-1 activity. In vivo, in a self-resolving zymosan A-induced peritonitis model, RvD2 blocked the NLRP3 inflammasome leading to reduced release of IL-1β into the exudates, repression of osteopontin, and MCP-1 expression and induction of M2 markers of resolution (i.e., CD206 and arginase-1) in peritoneal macrophages. RvD2 inhibitory actions were receptor mediated and were abrogated by a selective GPR18 antagonist. Together, these findings support the hypothesis that SPMs have the ability to inhibit the priming and to expedite the deactivation of the NLRP3 inflammasome in macrophages during the resolution process.

The influence of the N-terminal region proximal to the core domain on the assembly and chaperone activity of αB-crystallin.

αB-Crystallin (HSPB5) is a small heat-shock protein that is composed of dimers that then assemble into a polydisperse ensemble of oligomers. Oligomerisation is mediated by heterologous interactions between the C-terminal tail of one dimer and the core "α-crystallin" domain of another and stabilised by interactions made by the N-terminal region. Comparatively little is known about the latter contribution, but previous studies have suggested that residues in the region 54-60 form contacts that stabilise the assembly. We have generated mutations in this region (P58A, S59A, S59K, R56S/S59R and an inversion of residues 54-60) to examine their impact on oligomerisation and chaperone activity in vitro. By using native mass spectrometry, we found that all the αB-crystallin mutants were assembly competent, populating similar oligomeric distributions to wild-type, ranging from 16-mers to 30-mers. However, circular dichroism spectroscopy, intrinsic tryptophan and bis-ANS fluorescence studies demonstrated that the secondary structure differs to wild type, the 54-60 inversion mutation having the greatest impact. All the mutants exhibited a dramatic decrease in exposed hydrophobicity. We also found that the mutants in general were equally active as the wild-type protein in inhibiting the amorphous aggregation of insulin and seeded amyloid fibrillation of α-synuclein in vitro, except for the 54-60 inversion mutant, which was significantly less effective at inhibiting insulin aggregation. Our data indicate that alterations in the part of the N-terminal region proximal to the core domain do not drastically affect the oligomerisation of αB-crystallin, reinforcing the robustness of αB-crystallin in functioning as a molecular chaperone.

Tin Dioxide-Based Superacid Aerogels Produced Using Propylene Oxide

Tin dioxide-based aerogels were produced by supercritical drying of gels, synthesized using propylene oxide, in CO2 and isopropanol. Aerogels consisted of nanocrystalline cassiterite and had a specific surface area of 210–270 m2/g. Sulfation with sulfuryl chloride imparted superacidic properties to the aerogels (the Hammett acidity function H0 reached values within the range – 11.99 ≥ H0 ≥ –12.7). Superacid SnO2 aerogels demonstrated high catalytic activity in 1-hexene oligomerization and isomerization.