Hydrophobic Cage Research Articles

Facile synthesis and linker guided self-assembly of dendron-like amphiphiles

In this work, we studied the linker effect on the nanostructures of a serious of specifically designed, functionalized polyhedral oligomeric silsesquioxane (POSS) based Dendron-like macro-isomers. The varying linkers between hydrophilic and hydrophobic POSS cages lead to topological isomers with identical composition but different molecular shapes. Their unique phase behaviors highlight remarkable effects of molecular architectures on the formation of nanostructures. Due to topological constraints, these macro-isomers assume either a fan- or a cone-molecular shape, which assembles into either hexagonally packed cylindrical phase (HEX) or Frank-Kasper A15 phase. This work provides guiding rules on designing precise molecular nanostructures with desired properties via linker engineering.

Nanoparticles of Metal-Organic Cages Overcoming Drug Resistance in Ovarian Cancer.

A long-standing challenge in the treatment of ovarian cancer is drug resistance to standard platinum-based chemotherapy. Recently, increasing attention has been drawn to the use of self-assembled metal-organic complexes as novel therapeutics for cancer treatment. However, high hydrophobicity that is often associated with these structures lowers their solubility and hinders their clinical translation. In this article, we present a proof-of-concept study of using nanoprecipitation to formulate the hydrophobic metal-organic cages and facilitate their use in treating chemoresistant ovarian cancer. The Pt6L4 Cage 1 is an octahedral cage formed by self-assembly of six 1,10-phenanthroline-Pt(II) centers and four 2,4,6-tris(4-pyridyl)-1,3,5-triazine ligands (L). Cage 1 is able to trigger DNA damage and exhibits promising in vitro potency against a panel of human ovarian cancer cell lines. However, due to the large portion of aromatic components, this cage structure has very limited solubility in cell culture media (<20μM). Notably, upon nanoformulation by using fluorescein (2) and a pegylated anionic polymer (3), the concentration of Cage 1 can reach up to 0.4 mM. Production of the nanoparticles of metal-organic cages (nMOC) is driven by the formation of the 1:1 host-guest complex of 1 and 2 in aqueous solution, which then form nanoprecipitation in presence of poly glutamic acid-b-poly ethylene glycol (3). The resulted nMOC are about 100 nm in diameter, and they serve as a delivery platform that slowly releases the therapeutic content. The use of fluorescein facilitates monitoring cell entry of nMOC and drug release using flow cytometry. Finally, comparing to cisplatin, the nMOC exhibit comparable in vitro efficacy against a panel of human cancer cell lines, and notably, it shows a much lower resistance factor against chemoresistant ovarian cancer cell lines.

Structural elements of a pH-sensitive inhibitor binding site in NMDA receptors

Context-dependent inhibition of N-methyl-D-aspartate (NMDA) receptors has important therapeutic implications for the treatment of neurological diseases that are associated with altered neuronal firing and signaling. This is especially true in stroke, where the proton concentration in the afflicted area can increase by an order of magnitude. A class of allosteric inhibitors, the 93-series, shows greater potency against GluN1-GluN2B NMDA receptors in such low pH environments, allowing targeted therapy only within the ischemic region. Here we map the 93-series compound binding site in the GluN1-GluN2B NMDA receptor amino terminal domain and show that the interaction of the N-alkyl group with a hydrophobic cage of the binding site is critical for pH-dependent inhibition. Mutation of residues in the hydrophobic cage alters pH-dependent potency, and remarkably, can convert inhibitors into potentiators. Our study provides a foundation for the development of highly specific neuroprotective compounds for the treatment of neurological diseases.

Enhanced pervaporation performance of PDMS membranes based on nano-sized Octa[(trimethoxysilyl)ethyl]-POSS as macro-crosslinker

A homogeneous distribution of inorganic fillers and their integration with polymer matrix is the primary challenge for advancement of mixed matrix membranes (MMMs) in pervaporation. Due to well-defined structure and multi-functional groups attached to the apex silicon atoms, polyhedral oligomeric silsesquioxane (POSS) provides a high possibility of good compatibility with diverse polymer matrix at the molecular level. In this work, soluble and reactive octa[(trimethoxysilyl)ethyl]-POSS(OPS) was synthesized, which was used as macro-crosslinker and reinforced porous fillers of polydimethylsiloxane (PDMS) synchronously to prepare a series of OPS/PDMS MMMs. The OPS/PDMS MMMs were characterized by FT-IR, XRD, SEM, TGA, DSC, PALS, vapor adsorption measurement and tensile test. It was found that OPS dispersed homogeneously in PDMS matrix and achieved good integration with PDMS based on SEM and DSC characterization. PALS results indicated that compared with pure PDMS membrane, OPS/PDMS MMMs with proper OPS loading showed much larger radii of free volume cavities (r3, r4) and fractional free volumes (fv3, fv4 and fv). The numerous hydrophobic POSS cages and enlarged PDMS’ free volume would effectively improve the diffusion selectivity towards ethanol. Vapor adsorption results showed that the chemical incorporation of moderate amount OPS into PDMS not only improved ethanol vapor adsorption amount, but also depressed water adsorption amount in PDMS, which would obviously improve PDMS’ sorption selectivity to ethanol. As applied to the bio-ethanol recovery from aqueous solutions, the prepared OPS/PDMS MMMs exhibited a simultaneous increase in permeation flux and separation factor, breaking the permeation flux-separation factor trade-off limitation. As OPS loading was 7.5 wt%, the separation factor of OPS/PDMS MMMs reached the maximum value of 16.4 (109% higher than that of pure PDMS membrane), with permeation flux of 253.1 g/m2h (32% higher than that of pure PDMS membrane). Experimental results showed that an increase in operation temperature resulted in an increase in permeation flux, but decrease in permeability, separation factor and selectivity. The pervaporation performance of OPS/PDMS MMMs kept stable during two days operation time. This work may provide useful insights of high-performance MMMs with a POSS embedded selective layer for biofuel separation.

Inhibition of PP2A by hesperetin may contribute to Akt and ERK1/2 activation status in cortical neurons

Flavonoids and their metabolites are well reported to modulate the activation/phosphorylation of various cellular kinases, such as ERK1/2 and JNK, although the mechanism by which they do so is unclear. In this study, we investigated the impact of flavanones on the activation of PI3K/Akt and ERK1/2 and determine whether this is mediated, in part, by the inhibition of phosphatases. Primary cortical neurons were exposed to physiological concentrations of hesperetin and the phosphorylation status of the kinases PI3K/Akt and ERK1/2 and the phosphatases PP2A and PTEN were assessed by immunoblotting after 30 min. Exposure to 100–300 nM hesperetin led to significant increases in the phosphorylation of ERK1/2 and Akt and significant decreases in PP2A levels and enzyme activity. Using in silico docking, hesperetin was found to fit into the active site of PP2A interacting within the hydrophobic cage of the catalytic unit. These data suggest a potential mechanism by which flavanones may lead to increased activation of ERK1/2 and Akt, commonly observed in cell models. Their interaction with and inhibition of cellular phosphatases counteract normal physiological regulation of signaling pathway activation thus facilitating and/or maintaining the activation status of ERK1/2 and Akt, important regulators of brain functions.

(Invited) Paramagnetic Endohedral Fullerenes for Biomedical Applications

N@C60 is a paramagnetic endohedral fullerene species comprised of a single nitrogen atom incarcerated within a C60 carbon cage. Shielding of the nitrogen from the external environment results in extremely long relaxation times of its electron spin (T1 = 0.375 ms, T2 = 0.25 ms). This provides the molecule with a very sharp EPR signal,1 which undergoes observable dipolar broadening in the presence of other paramagnetic species, suggesting that N@C60 derivatives would be ideal candidates as spin probes for biological applications.2–4 In order for this to be realised functionalisation of the inherently hydrophobic fullerene cage must be undertaken to render it compatible with aqueous environments. Several methodologies for the solubilisation of empty cage and other endohedral fullerene species have been demonstrated,5–7 however many of these are unsuitable for use with N@C60 due to its instability at elevated temperatures.8 Herein we report the first examples of water-soluble derivatives of N@C60, prepared using an adaptation of the widely used Bingel reaction.9 Preliminary investigations towards the use of these materials as electron paramagnetic resonance imaging (EPRI) agents is also discussed.10 1 J. J. L. Morton, A. M. Tyryshkin, A. Ardavan, K. Porfyrakis, S. A. Lyon and G. Andrew D. Briggs, J. Chem. Phys., 2006, 124, 014508. 2 K.-P. Dinse, H. Käß, C. Knapp and N. Weiden, Carbon, 2000, 38, 1635–1640. 3 G. Liu, A. N. Khlobystov, G. Charalambidis, A. G. Coutsolelos, G. A. D. Briggs and K. Porfyrakis, J. Am. Chem. Soc., 2012, 134, 1938–1941. 4 S. Zhou, M. Yamamoto, G. A. D. Briggs, H. Imahori and K. Porfyrakis, J. Am. Chem. Soc., 2016, 138, 1313–1319. 5 J. Li, A. Takeuchi, M. Ozawa, X. Li, K. Saigo and K. Kitazawa, J. Chem. Soc. Chem. Commun., 1993, 0, 1784–1785. 6 M. Brettreich and A. Hirsch, Tetrahedron Lett., 1998, 39, 2731–2734. 7 I. Rašović, Mater. Sci. Technol., 2016, 0, 1–18. 8 A. Iwasiewicz-Wabnig, K. Porfyrakis, G. A. D. Briggs and B. Sundqvist, Phys. Status Solidi B, 2009, 246, 2767–2770. 9 S. Zhou, I. Rašović, G. A. D. Briggs and K. Porfyrakis, Chem. Commun., 2015, 51, 7096–7099. 10 S. P. Cornes, S. Zhou and K. Porfyrakis, Chem. Commun., 2017, DOI:10.1039/C7CC07106J. Figure 1

Markov-state model for CO2 binding with carbonic anhydrase under confinement.

Enzyme immobilization with a nanostructure material can enhance its stability and facilitate reusability. However, the apparent activity is often compromised due to additional diffusion barriers and complex interactions with the substrates and solvent molecules. The present study elucidates the effects of the surface hydrophobicity of nano-confinement on CO2 diffusion to the active site of human carbonic anhydrase II (CA), an enzyme that is able to catalyze CO2 hydration at extremely high turnover rates. Using the Markov-state model in combination with coarse-grained molecular dynamics simulations, we demonstrate that a hydrophobic cage increases CO2 local density but hinders its diffusion towards the active site of CA under confinement. By contrast, a hydrophilic cage hinders CO2 adsorption but promotes its binding with CA. An optimal surface hydrophobicity can be identified to maximize both the CO2 occupation probability and the diffusion rate. The simulation results offer insight into understanding enzyme performance under nano-confinement and help us to advance broader applications of CA for CO2 absorption and recovery.

Hierarchical Self-Organization of AB n Dendron-like Molecules into a Supramolecular Lattice Sequence.

To understand the hierarchical self-organization behaviors of soft materials as well as their dependence on molecular geometry, a series of ABn dendron-like molecules based on polyhedral oligomeric silsesquioxane (POSS) nanoparticles were designed and synthesized. The apex of these molecules is a hydrophilic POSS cage with 14 hydroxyl groups (denoted DPOSS). At its periphery, there are different numbers (n = 1–8) of hydrophobic POSS cages with seven isobutyl groups (denoted BPOSS), connected to the apical DPOSS via flexible dendron type linker(s). By varying the BPOSS number from one to seven, a supramolecular lattice formation sequence ranging from lamella (DPOSS-BPOSS), double gyroid (space group of Ia3̅d, DPOSS-BPOSS2), hexagonal cylinder (plane group of P6mm, DPOSS-BPOSS3), Frank–Kasper A15 (space group of Pm3̅n, DPOSS-BPOSS4, DPOSS-BPOSS5, and DPOSS-BPOSS6), to Frank–Kasper sigma (space group of P42/mnm, DPOSS-BPOSS7) phases can be observed. The nanostructure formations in this series of ABn dendron-like molecules are mainly directed by the molecular geometric shapes. Furthermore, within each spherical motif, the spherical core consists hydrophilic DPOSS cages with flexible linkages, while the hydrophobic BPOSS cages form the relative rigid shell, and contact with neighbors to provide decreased interfaces among the spherical motifs for constructing final polyhedral motifs in these Frank–Kasper lattices. This study provides the design principle of molecules with specific geometric shapes and functional groups to achieve anticipated structures and macroscopic properties.

Biomedical Applications of Metal-Encapsulated Fullerene Nanoparticles.

The carbonaceous nanomaterials known as metallofullerenes have attracted considerable attention due to their attractive properties. The robust nature of the "Trojan Horse" fullerene cage provides an important structural component, which isolates the metal cluster from the bioenvironment. The large carbon surface area is ideally suited for multiple exo-functionalization approaches to modify the hydrophobic cage for a more hydrophilic bioenvironment. Additionally, peptides and other agents are readily covalently attached to this nanoprobe for targeting applications. The recent progress in developing metallofullerenes for next-generation biomedical applications is described. Of special interest are magnetic resonance imaging (MRI) contrast agents. Several recent studies reported cumulative gadolinium deposition in the brain and bones of individuals using commercial clinical MRI contrast agents. Gadolinium-based metallofullerenes provide 2-3 orders of magnitude improvement in MRI relaxivity and potentially lower clinical levels of toxic Gd3+ ions deposited. Other potential biomedical applications are also reviewed herein.

Skp is a multivalent chaperone of outer-membrane proteins.

The trimeric chaperone Skp sequesters outer membrane proteins (OMPs) within a hydrophobic cage, preventing their aggregation during transport across the periplasm in Gram negative bacteria. Here, we study the interaction between Escherichia coli Skp and five OMPs of varying size. Investigations of the kinetics of OMP folding reveal that greater Skp:OMP ratios are required to prevent the folding of 16-stranded OMPs compared with their 8-stranded counterparts. Ion mobility spectrometry-mass spectrometry (IMS-MS) data, computer modelling and molecular dynamics simulations provide evidence that 10- to 16-stranded OMPs are encapsulated within an expanded Skp substrate cage. For OMPs which cannot be fully accommodated in the expanded cavity, sequestration is achieved by binding of an additional Skp trimer. The results suggest a new mechanism for Skp chaperone activity involving coordination of multiple copies of Skp to protect a single substrate from aggregation.

Polystyrene-Core-Silica-Shell Hybrid Particles Containing Gold and Magnetic Nanoparticles.

Polystyrene-core-silica-shell hybrid particles were synthesized by combining the self-assembly of nanoparticles and the polymer with a silica coating strategy. The core-shell hybrid particles are composed of gold-nanoparticle-decorated polystyrene (PS-AuNP) colloids as the core and silica particles as the shell. PS-AuNP colloids were generated by the self-assembly of the PS-grafted AuNPs. The silica coating improved the thermal stability and dispersibility of the AuNPs. By removing the "free" PS of the core, hollow particles with a hydrophobic cage having a AuNP corona and an inert silica shell were obtained. Also, Fe3O4 nanoparticles were encapsulated in the core, which resulted in magnetic core-shell hybrid particles by the same strategy. These particles have potential applications in biomolecular separation and high-temperature catalysis and as nanoreactors.

Cationic M2L4cages for perchlorate removal from aqueous solutions and preferential perchlorate incorporation in hydrophilic solutions

Four new cage-type compounds, [A ⊂ Cu2(m-bbitrb)4]A3 (A = Cl− (1a), Br− (1b), m-bbitrb = 1,3-bis(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene), and [SO4 ⊂ Cu2(m-bbitrb)4]A2 (A = Cl− (2a), Br− (2b)), were synthesized and characterized. These compounds have a M2L4-type cationic cage, incorporating an anion in the cage. Although the four compounds are insoluble in water, they exhibit ClO4− removal activity from aqueous solutions by exchange with anions located outside the cage. The [Cl ⊂ Cu2(m-bbitrb)4]3+ cage removes ClO4− from aqueous solutions preferentially. To study the selective removal process by the cationic cage, the affinity of the [Cu2(m-bbitrb)4]4+ cage for ClO4− was studied by acquiring the solid-state reflectance spectra, absorption spectra, and ESI-TOF mass spectra in solutions of MeCN and MeCN/H2O for [SO4 ⊂ Cu2(m-bbitrb)4](ClO4)2 (2d). The results indicated that the SO42− in [SO4 ⊂ Cu2(m-bbitrb)4]2+ was retained in the MeCN solution, whereas in the MeCN/H2O solution the SO42− was exchanged with the ClO4− located outside the cage. This is because an increase in the hydrophilicity of the solution promotes the incorporation of hydrophobic ClO4− into the hydrophobic cage, meaning that the preferential removal of ClO4− from aqueous solutions is due to the higher affinity of the hydrophobic space created outside the M2LB4 cages in the solid state.

C₆₀-dyad aggregates: self-organized structures in aqueous solutions.

Extensive full-atomistic molecular dynamics simulations are performed to study the self-organization of C60-fullerene dyad molecules in water, namely phenyl-C61-butyric acid methyl ester and fulleropyrrolidines, which have two elements of ordering, the hydrophobic fullerene cage and the hydrophilic/ionic group. While pristine fullerene or phenyl-C61-butyric acid methyl ester forms spherical droplets in order to minimize the surface tension, the amphiphilic nature of charged solute molecules leads to the formation of supramolecular assemblies having cylindrical shape driven by charge repulsion between the ionic groups located on the surface of the aggregates. We show that formation of non-spherical micelles is the geometrical consequence if the fullerene derivatives are considered as surfactants where the ionized groups are only hydrophilic unit. The agglomeration behavior of fullerenes is evaluated by determining sizes of the clusters, solvent accessible surface areas, and shape parameters. By changing the size of the counterions from chloride over iodide to perchlorate we find a thickening of the cylinder-like structures which can be explained by stronger condensation of larger ions and thus partial screening of the charge repulsion on the cluster surface. The reason for the size dependence of counterion condensation is the formation of a stronger hydration shell in case of small ions which in turn are repelled from the fullerene aggregates. Simulations are also in good agreement with the experimentally observed morphologies of decorated C60-nanoparticles.

The effect of alcohol concentration on the mass signal of CO2 detected by differential mass spectrometry

Differential electrochemical mass spectrometry (DEMS) is one of the powerful techniques for quantitative analysis of multiple products and their distribution from complex reactions occurred at the electrode/electrolyte interface, in which precise calibration of the mass signal is a prerequisite for accurate determination of product rate and current efficiencies of various products. In this work, we report the effect of alcohol concentration on the detected DEMS signal of CO2, a common final product from electrochemical oxidation of small organic molecules. Comparing to the solution with low alcohol concentration and the same CO2 concentration, we observe a significant reduction of mass signal of CO2 in a concentrated methanol or ethanol solution (>0.1M). Possible origins for this are: 1) alcohol molecules evaporate into the vacuum chamber and reduce the ionization probability for CO2 via competition for electrons; and 2) CO2 is trapped in the hydrophobic alcohol cages formed in the aqueous electrolyte. A proper way to eliminate alcohol concentration effect on the detected CO2 mass signal in DEMS studies on fuel cell related electrocatalysis is suggested.

Using FTIR spectroscopy to study the phase transitions of poly(N-isopropylacrylamide) in tetrahydrofuran-d 8/D2O

In this study we used Fourier transform infrared (FTIR) spectroscopy to investigate the phase behavior of poly(N-isopropylacrylamide) (PNIPAM) in mixed solvents comprising D2O and tetrahydrofuran-d 8(THF-d8). The signals of the CH3 groups of the N-isopropyl amide unit and the CH2 groups on the main chain and those in the amide I region of the PNIPAM provided details about the various hydrophobic and hydrophilic interactions in the mixed aqueous solution. Upon increasing the volume fraction of THF-d 8 (x v) from 0 to 11 %, coil-to-globule transition occurred as a result of dehydration and hydrophobic interactions among the hydrophobic groups of the PNIPAM chain, followed by induced aggregation and collapse of the PNIPAM chain. When the value of x v was in the range of 11 to 55 % the hydrophobic groups formed hydrophobic cages that prevented diffusion of D2O molecules and the formation of hydrogen bonds with the amide I units of the PNIPAM chains. Meanwhile, the hydration sphere of THF-d 8 also hindered the hydrophobic–hydrophobic interactions between THD-d 8 and the PNIPAM; consequently, the PNIPAM chains shrank as they aggregated. The PNIPAM solution was homogenized again at values of x v greater than 55 %, due to hydrophobic–hydrophobic interactions among the free THD-d 8 molecules and the hydrophobic groups of the PNIPAM. We believe that dehydration of the hydrophobic groups rather than inter- and intrachain hydrogen bonding was the major driving force behind the aggregation and coil-to-globule transitions.

Assembly of Amphiphilic Baskets into Stimuli-Responsive Vesicles. Developing a Strategy for the Detection of Organophosphorus Chemical Nerve Agents

We designed basket 1 to comprise a C3-symmetric hydrophobic cage (477 Å(3)) at its southern edge and three polar ammonium caps at the northern edge. This amphiphilic molecule was observed to assemble into large unilamellar vesicles (350 nm, TEM) in water and thereby entrap dimethyl phenylphosphonate (184 Å(3)) in its cavity (K(app) = (1.97 ± 0.02) × 10(3) M(-1)). The entrapment of the organophosphonate, akin to soman in size (186 Å(3)), triggers the transformation of the vesicular material into nanoparticles (100 nm, TEM). Stimuli-responsive vesicles, containing baskets of type 1 in their bilayer membrane, are unique assemblies and important for obtaining novel sensing devices.

Folding Dynamics of the Trp-Cage Miniprotein: Evidence for a Native-Like Intermediate from Combined Time-Resolved Vibrational Spectroscopy and Molecular Dynamics Simulations

Trp-cage is a synthetic 20-residue miniprotein which folds rapidly and spontaneously to a well-defined globular structure more typical of larger proteins. Due to its small size and fast folding, it is an ideal model system for experimental and theoretical investigations of protein folding mechanisms. However, Trp-cage's exact folding mechanism is still a matter of debate. Here we investigate Trp-cage's relaxation dynamics in the amide I' spectral region (1530-1700 cm(-1)) using time-resolved infrared spectroscopy. Residue-specific information was obtained by incorporating an isotopic label ((13)C═(18)O) into the amide carbonyl group of residue Gly11, thereby spectrally isolating an individual 310-helical residue. The folding-unfolding equilibrium is perturbed using a nanosecond temperature-jump (T-jump), and the subsequent re-equilibration is probed by observing the time-dependent vibrational response in the amide I' region. We observe bimodal relaxation kinetics with time constants of 100 ± 10 and 770 ± 40 ns at 322 K, suggesting that the folding involves an intermediate state, the character of which can be determined from the time- and frequency-resolved data. We find that the relaxation dynamics close to the melting temperature involve fast fluctuations in the polyproline II region, whereas the slower process can be attributed to conformational rearrangements due to the global (un)folding transition of the protein. Combined analysis of our T-jump data and molecular dynamics simulations indicates that the formation of a well-defined α-helix precedes the rapid formation of the hydrophobic cage structure, implying a native-like folding intermediate, that mainly differs from the folded conformation in the orientation of the C-terminal polyproline II helix relative to the N-terminal part of the backbone. We find that the main free-energy barrier is positioned between the folding intermediate and the unfolded state ensemble, and that it involves the formation of the α-helix, the 310-helix, and the Asp9-Arg16 salt bridge. Our results suggest that at low temperature (T ≪ Tm) a folding path via formation of α-helical contacts followed by hydrophobic clustering becomes more important.

Recognition of the Thomsen-Friedenreich Pancarcinoma Carbohydrate Antigen by a Lamprey Variable Lymphocyte Receptor

Variable lymphocyte receptors (VLRs) are leucine-rich repeat proteins that mediate adaptive immunity in jawless vertebrates. VLRs were recently shown to recognize glycans, such as the tumor-associated Thomsen-Friedenreich antigen (TFα; Galβ1-3GalNAcα), with a selectivity rivaling or exceeding that of lectins and antibodies. To understand the basis for TFα recognition by one such VLR (VLRB.aGPA.23), we measured thermodynamic parameters for the binding interaction and determined the structure of the VLRB.aGPA.23-TFα complex to 2.2 Å resolution. In the structure, four tryptophan residues form a tight hydrophobic cage encasing the TFα disaccharide that completely excludes buried water molecules. This cage together with hydrogen bonding of sugar hydroxyls to polar side chains explains the exquisite selectivity of VLRB.aGPA.23. The topology of the glycan-binding site of VLRB.aGPA.23 differs markedly from those of lectins or antibodies, which typically consist of long, convex grooves for accommodating the oligosaccharide. Instead, the TFα disaccharide is sandwiched between a variable loop and the concave surface of the VLR formed by the β-strands of the leucine-rich repeat modules. Longer oligosaccharides are predicted to extend perpendicularly across the β-strands, requiring them to bend to match the concavity of the VLR solenoid.

Structural Basis of Recruitment of DNA Polymerase ζ by Interaction between REV1 and REV7 Proteins

REV1, REV3, and REV7 are pivotal proteins in translesion DNA synthesis, which allows DNA synthesis even in the presence of DNA damage. REV1 and REV3 are error-prone DNA polymerases and function as inserter and extender polymerases in this process, respectively. REV7 interacts with both REV1 and REV3, acting as an adaptor that functionally links the two, although the structural basis of this collaboration remains unclear. Here, we show the crystal structure of the ternary complex, composed of the C-terminal domain of human REV1, REV7, and a REV3 fragment. The REV1 C-terminal domain adopts a four-helix bundle that interacts with REV7. A linker region between helices 2 and 3, which is conserved among mammals, interacts with the β-sheet of REV7. Remarkably, the REV7-binding interface is distinct from the binding site of DNA polymerase η or κ. Thus, the REV1 C-terminal domain might facilitate polymerase switching by providing a scaffold for both inserter and extender polymerases to bind. Our structure reveals the basis of DNA polymerase ζ (a complex of REV3 and REV7) recruitment to the stalled replication fork and provides insight into the mechanism of polymerase switching.

Lipophilic Isosteres of a π-π Stacking Interaction: New Inhibitors of the Bcl-2-Bak Protein-Protein Interaction.

The discovery of new Bcl-2 protein-protein interaction antagonists is described. We replaced the northern fragment of ABT737 (π-π stacking interactions) with structurally simplified hydrophobic cage structures with much reduced conformational flexibility and rotational freedom. The binding mode of the compounds was elucidated by X-ray crystallography, and the compounds showed excellent oral bioavailability and clearance in rat PK studies.