Pathway Dependence of the Formation and Development of Prefibrillar Aggregates in Insulin B Chain

Amyloid fibrils have been an important subject as they are involved in the development of many amyloidoses and neurodegenerative diseases. The formation of amyloid fibrils is typically initiated by nucleation, whereas its exact mechanisms are largely unknown. With this situation, we have previously identified prefibrillar aggregates in the formation of insulin B chain amyloid fibrils, which have provided an insight into the mechanisms of protein assembly involved in nucleation. Here, we have investigated the formation of insulin B chain amyloid fibrils under different pH conditions to better understand amyloid nucleation mediated by prefibrillar aggregates. The B chain showed strong propensity to form amyloid fibrils over a wide pH range, and prefibrillar aggregates were formed under all examined conditions. In particular, different structures of amyloid fibrils were found at pH 5.2 and pH 8.7, making it possible to compare different pathways. Detailed investigations at pH 5.2 in comparison with those at pH 8.7 have suggested that the evolution of protofibril-like aggregates is a common mechanism. In addition, different processes of evolution of the prefibrillar aggregates have also been identified, suggesting that the nucleation processes diversify depending on the polymorphism of amyloid fibrils.     

Protein side chain modeling with orientation-dependent atomic force fields derived by series expansions

We describe the development of new force fields for protein side chain modeling called optimized side chain atomic energy (OSCAR). The distance‐dependent energy functions (OSCAR‐d) and side‐chain dihedral angle potential energy functions were represented as power and Fourier series, respectively. The resulting 802 adjustable parameters were optimized by discriminating the native side chain conformations from non‐native conformations, using a training set of 12,000 side chains for each residue type. In the course of optimization, for every residue, its side chain was replaced by varying rotamers, whereas conformations for all other residues were kept as they appeared in the crystal structure. Then, the OSCAR‐d were multiplied by an orientation‐dependent function to yield OSCAR‐o. A total of 1087 parameters of the orientation‐dependent energy functions (OSCAR‐o) were optimized by maximizing the energy gap between the native conformation and subrotamers calculated as low energy by OSCAR‐d. When OSCAR‐o with optimized parameters were used to model side chain conformations simultaneously for 218 recently released protein structures, the prediction accuracies were 88.8% for χ₁, 79.7% for χ_{1 + 2}, 1.24 Å overall root mean square deviation (RMSD), and 0.62 Å RMSD for core residues, respectively, compared with the next‐best performing side‐chain modeling program which achieved 86.6% for χ₁, 75.7% for χ_{1 + 2}, 1.40 Å overall RMSD, and 0.86 Å RMSD for core residues, respectively. The continuous energy functions obtained in this study are suitable for gradient‐based optimization techniques for protein structure refinement. A program with built‐in OSCAR for protein side chain prediction is available for download at http://sysimm.ifrec.osaka‐u.ac.jp/OSCAR/ . © 2011 Wiley Periodicals, Inc. J Comput Chem 2011     

Cold Denaturation of α‐Synuclein Amyloid Fibrils

Although amyloid fibrils are associated with numerous pathologies, their conformational stability remains largely unclear. Herein, we probe the thermal stability of various amyloid fibrils. α‐Synuclein fibrils cold‐denatured to monomers at 0–20 °C and heat‐denatured at 60–110 °C. Meanwhile, the fibrils of β2‐microglobulin, Alzheimer’s Aβ1‐40/Aβ1‐42 peptides, and insulin exhibited only heat denaturation, although they showed a decrease in stability at low temperature. A comparison of structural parameters with positive enthalpy and heat capacity changes which showed opposite signs to protein folding suggested that the burial of charged residues in fibril cores contributed to the cold denaturation of α‐synuclein fibrils. We propose that although cold‐denaturation is common to both native proteins and misfolded fibrillar states, the main‐chain dominated amyloid structures may explain amyloid‐specific cold denaturation arising from the unfavorable burial of charged side‐chains in fibril cores.     

Identification of Regions in Apomyoglobin that Form Intermolecular Interactions in Amyloid Aggregates Using High-Performance Mass Spectrometry

The formation of amyloid aggregates in human organs and tissues causes the development of incurable diseases. However, experimental studies of the mechanism of amyloid formation by proteins and the structural characteristics of amyloids are complicated because of the heterogeneity and high molecular weight of the aggregates. We used limited proteolysis and mass spectrometry for the identification of regions in the apomyoglobin polypeptide chain, which give rise to intermolecular interactions in amyloid structures. Tandem mass spectroscopy enabled the identification of regions in the myoglobin polypeptide chain, which form the core of amyloid structures. It was shown that the main structural elements for the formation of the core of amyloid fibrils in myoglobin were regions from 60 through 90 and from 97 through 124 amino acid residues. These regions coincide well with those theoretically predicted. This approach yielded important data on the structure of protein molecules in aggregates and on conformational rearrangements of apomyoglobin upon amyloid formation.     

Effects of cysteic acid groups on the gas-phase reactivity and dissociation of [M + 4H]4+ ions from insulin chain B

Gas-phase ion/molecule reactions and collision-induced dissociation (CID) were conducted on [M + 4H]4+ of insulin chain B. This Fourier transform mass spectrometry work involved ions from the oxidized peptide (with two cysteic acid residues) and its reduced form (with two cysteine residues). Kinetic behavior during deprotonation and hydrogen/deuterium exchange reactions indicates that insulin B (ox) ions have two distinct structural types. In contrast, insulin B (red) ions have only one major reacting population, which has a more compact structure than the oxidized ions. No significant differences in fragmentation patterns for the two insulin B (ox) populations were observed when CID was performed as a function of deprotonating reaction time. However, markedly different fragmentation was found between [M + 4H]4+ of insulin B (ox) and (red). Therefore, the presence of cysteic acid groups in insulin B (ox) significantly impacts dissociation and presumably structure. This suggests that some insulin B (ox) ions are zwitterionic, with the five basic sites protonated and one cysteic acid group deprotonated. Molecular dynamics calculations revealed several viable structures that are consistent with the experimental results. For example, the most stable form of the reduced ion, which is unprotonated at the His10, is very compact and has lost the alpha-helix of native insulin. Low energy structures for the oxidized ions include a zwitterion with an intraionic interaction between anionic Cyx7 and cationic His10, as well as a nonzwitterionic conformer that lacks a proton at Phe1; both structures retain the alpha-helix. These structures may account for the two experimentally observed isomers, although others are possible. In addition, experiments on oxidized insulin B were conducted from methanolic solution, which may denature the conformation, and pure aqueous solution, which may leave a native conformation. These differences in solvent composition had no effect on the gas-phase results.     

酚化合物对胰岛素淀粉样纤维化的抑制作用

采用牛胰岛素作为模型多肽分子, 对几种结构相近的简单多酚的抗多肽淀粉样纤维化作用进行了研究. 结果表明, 邻苯二酚和对苯二酚对胰岛素纤维化具有抑制作用, 并通过形成醌中间体对多肽链进行修饰, 与对苯醌作用类似; 而苯酚和间二苯酚在相同条件下, 既不能修饰多肽也无抑制纤维化作用. 在无氧条件下, 邻苯二酚和对苯二酚对胰岛素纤维化的抑制作用明显降低, 说明酚化合物经氧化形成的醌中间体是其抗胰岛素纤维化的主要活性结构.     

Efficient Production of γ-GABA Using Recombinant <Emphasis Type="Italic">E. coli</Emphasis> Expressing Glutamate Decarboxylase (GAD) Derived from Eukaryote <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

A cellulase-producing bacterium, designated as strain AK9, was isolated from a hot spring of Tatta Pani, Azad Kashmir, Pakistan. The bacterium was identified as Bacillus amyloliquefaciens through 16S rRNA sequencing. Cellulase from strain AK9 was able to liberate glucose from soluble cellulose and carboxymethyl cellulose (CMC). Enzyme was purified through size exclusion chromatography and a single band of ～47 kDa was observed on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The enzyme was purified with recovery of 35.5%, 3.6-fold purity with specific activity of 31 U mg^?1. The purified cellulase retained its activity over a wide range of temperature (50–70 °C) and pH (3–7) with maximum stability at 60 °C and pH 5.0. The activity inhibited by ethylenediaminetetraacetic acid (EDTA), suggested that it was metalloenzyme. Diethyl pyrocarbonate (DEPC) and β-mercaptoethanol significantly inhibited cellulase activity that revealed the essentiality of histidine residues and disulfide bonds for its catalytic function. It was stable in non-ionic surfactants, in the presence of various metal ions, and in water-insoluble organic solvents. Approximately 9.1% of reducing sugar was released after enzymatic saccharification of DAP-pretreated agro-residue, compared to a very low percentage by autohydrolysis treatment. Hence, it is concluded that cellulase from B. amyloliquefaciens AK9 can potentially be used in bioconversion of lignocellulosic biomass to fermentable sugars.     

Combined nuclear magnetic resonance spectroscopy and molecular dynamics study of growth hormone releasing hexapeptide GHRP‐6 and a cyclic analogue

The Growth Hormone Releasing Hexapeptide, GHRP‐6 was the first of a family of synthetic peptides that enhance the release of the Growth Hormone by the pituitary gland in a dose‐dependent manner. Since its discovery, it has been used as a benchmark and starting point in numerous researches aiming to obtain new drugs. Complete resonance assignment of GHRP‐6 NMR spectra in both open and cyclic forms are reported, showing some differences to random coil chemical shifts. Connectivities observed in the ROESY spectra indicate spatial proximity between the aromatic residues side‐chains in both molecules, as well as between residues DPhe5 and Lys6 sidechains. An ensemble of 10 structures was generated for each one of the molecules, showing RMSD values indicative of nonrandom structures. Molecular Dynamics simulations, both with and without explicit solvent, were carried out for GHRP‐6 and its cyclic analogue. Conformational analysis performed on the trajectories showed a nonrandom structure with a well preserved backbone. The presence of geometrical patterns resembling those typical of π‐π interactions in both peptides, suggest that this kind of interactions may be relevant for the biological activity of GHRP‐6. Same conclusion can be drawn from the spatial proximity of residues DPhe5 and Lys6 sidechains. Copyright © 2012 John Wiley & Sons, Ltd.     

Probing folded and unfolded states of outer membrane protein a with steady-state and time-resolved tryptophan fluorescence

Steady-state and time-resolved fluorescence measurements on each of five native tryptophan residues in full-length and truncated variants of E. coli outer-membrane protein A (OmpA) have been made in folded and denatured states. Tryptophan singlet excited-state lifetimes are multiexponential and vary among the residues. In addition, substantial increases in excited-state lifetimes accompany OmpA folding, with longer lifetimes in micelles than in phospholipid bilayers. This finding suggests that the Trp environments of OmpA folded in micelles and phospholipid bilayers are different. Measurements of Trp fluorescence decay kinetics with full-length OmpA folded in brominated lipid vesicles reveal that W102 is the most distant fluorophore from the hydrocarbon core, while W7 is the closest. Steady-state and time-resolved polarized fluorescence measurements indicate reduced Trp mobility when OmpA is folded in a micelle, and even lower mobility when the protein is folded in a bilayer. The fluorescence properties of truncated OmpA, in which the soluble periplasmic domain is removed, only modestly differ from those of the full-length form, suggesting similar folded structures for the two forms under these conditions.     

The non-isothermal kinetics of mullite formation in boehmite–zircon mixtures

In this work, we studied the kinetics of mullite formation in different composites under non-isothermal conditions using DTA. Different composites based of mullite, alumina, zircon and zirconia were prepared by reaction sintering of boehmite (as alumina source) and zircon. Several mixtures were used while varying the percentage of the boehmite from 30 to 70 mass% with a step of 10. Five compositions marked as B30, B40, B50, B60 and B70 corresponding to boehmite–zircon ratios (mass%) of 30/70, 40/60, 50/50, 60/40 and 70/30 were fabricated and studied. The DTA conducted at heating rates of 10, 20 and 30 K min^?1 showed an endothermic peak in all composites at about 1,603 K associated with mullite formation. The activation energies measured from non-isothermal treatments for five compositions (30, 40, 50, 60 and 70 mass% of boehmite) were 1,029, 1,085, 1,262, 1,508 and 1,321 kJ mol^?1, respectively. The n values (Avrami parameter) for all compositions are larger than 2.5, the mullite crystallization of these composites is followed by three-dimensional growth.     

SPICKER: a clustering approach to identify near-native protein folds

We have developed SPICKER, a simple and efficient strategy to identify near-native folds by clustering protein structures generated during computer simulations. In general, the most populated clusters tend to be closer to the native conformation than the lowest energy structures. To assess the generality of the approach, we applied SPICKER to 1489 representative benchmark proteins 相似文献   

Improved pose and affinity predictions using different protocols tailored on the basis of data availability

The D3R 2015 grand drug design challenge provided a set of blinded challenges for evaluating the applicability of our protocols for pose and affinity prediction. In the present study, we report the application of two different strategies for the two D3R protein targets HSP90 and MAP4K4. HSP90 is a well-studied target system with numerous co-crystal structures and SAR data. Furthermore the D3R HSP90 test compounds showed high structural similarity to existing HSP90 inhibitors in BindingDB. Thus, we adopted an integrated docking and scoring approach involving a combination of both pharmacophoric and heavy atom similarity alignments, local minimization and quantitative structure activity relationships modeling, resulting in the reasonable prediction of pose [with the root mean square deviation (RMSD) values of 1.75 Å for mean pose 1, 1.417 Å for the mean best pose and 1.85 Å for the mean all poses] and affinity (ROC AUC = 0.702 at 7.5 pIC50 cut-off and R = 0.45 for 180 compounds). The second protein, MAP4K4, represents a novel system with limited SAR and co-crystal structure data and little structural similarity of the D3R MAP4K4 test compounds to known MAP4K4 ligands. For this system, we implemented an exhaustive pose and affinity prediction protocol involving docking and scoring using the PLANTS software which considers side chain flexibility together with protein–ligand fingerprints analysis assisting in pose prioritization. This protocol through fares poorly in pose prediction (with the RMSD values of 4.346 Å for mean pose 1, 4.69 Å for mean best pose and 4.75 Å for mean all poses) and produced reasonable affinity prediction (AUC = 0.728 at 7.5 pIC50 cut-off and R = 0.67 for 18 compounds, ranked 1st among 80 submissions).     

Synthesis and mesomorphic properties of new chiral banana‐shaped liquid crystals with chiral 3‐(alkoxy)propoxy terminal groups

New chiral banana‐shaped liquid crystals with chiral 3‐(alkoxy)propoxy terminal groups (Pn‐O‐PIMB5*‐4O, n = 7, 8, 9 and 10) were synthesized and their mesomorphic properties and phase structures investigated by means of electro‐optic measurements, polarizing optical microscopy, differential scanning calorimetry, and second harmonic generation measurements. Most of these chiral bent‐core mesogens (n = 7–9) showed the antiferroelectric B2 phase, whereas P10‐O‐PIMB5*‐4O exhibited the B7 phase. Comparing with the previously reported homologue Pn‐O‐PIMB(n‐2)*, we conclude that the terminal chain structure, particularly the position of chiral centres, plays an important role in the emergence of particular phase structures.     

LEAP: Highly accurate prediction of protein loop conformations by integrating coarse‐grained sampling and optimized energy scores with all‐atom refinement of backbone and side chains

Prediction of protein loop conformations without any prior knowledge (ab initio prediction) is an unsolved problem. Its solution will significantly impact protein homology and template‐based modeling as well as ab initio protein‐structure prediction. Here, we developed a coarse‐grained, optimized scoring function for initial sampling and ranking of loop decoys. The resulting decoys are then further optimized in backbone and side‐chain conformations and ranked by all‐atom energy scoring functions. The final integrated technique called loop prediction by energy‐assisted protocol achieved a median value of 2.1 Å root mean square deviation (RMSD) for 325 12‐residue test loops and 2.0 Å RMSD for 45 12‐residue loops from critical assessment of structure‐prediction techniques (CASP) 10 target proteins with native core structures (backbone and side chains). If all side‐chain conformations in protein cores were predicted in the absence of the target loop, loop‐prediction accuracy only reduces slightly (0.2 Å difference in RMSD for 12‐residue loops in the CASP target proteins). The accuracy obtained is about 1 Å RMSD or more improvement over other methods we tested. The executable file for a Linux system is freely available for academic users at http://sparks‐lab.org . © 2013 Wiley Periodicals, Inc.     

Structural changes in the monomeric despentapeptide (B30-B26) insulin crystal

Insulin modified by the removal of its 5 B chain C terminal residues is monomeric but remains substantially potent. The crystal structures of the beef and insulin (dpi) with two molecules in the asymmetric unit has been determined by x-ray analysis. The 3-dimensional structure ofdpi proves to be generally similar to that of native molecule in 2Zn insulin. More detailed comparison reveals that the slight differences in the two independent molecules of beefdpi are distributed uniformly throughout the structure in contrast to insulin in 2Zn insulin, where the structural changes are concentrated in specific regions. The loss of symmetry in thedpi crystal appears to be the inability of the A9 serine to pack effectively in the C2 cell. The efficient packing of the sheepdpi molecule whose crystal structure has also been determined and where A9 is glycine supports this conclusion.     

Computational prediction of kink properties of helices in membrane proteins

We have combined molecular dynamics simulations and fold identification procedures to investigate the structure of 696 kinked and 120 unkinked transmembrane (TM) helices in the PDBTM database. Our main aim of this study is to understand the formation of helical kinks by simulating their quasi-equilibrium heating processes, which might be relevant to the prediction of their structural features. The simulated structural features of these TM helices, including the position and the angle of helical kinks, were analyzed and compared with statistical data from PDBTM. From quasi-equilibrium heating processes of TM helices with four very different relaxation time constants, we found that these processes gave comparable predictions of the structural features of TM helices. Overall, 95 % of our best kink position predictions have an error of no more than two residues and 75 % of our best angle predictions have an error of less than 15°. Various structure assessments have been carried out to assess our predicted models of TM helices in PDBTM. Our results show that, in 696 predicted kinked helices, 70 % have a RMSD less than 2 Å, 71 % have a TM-score greater than 0.5, 69 % have a MaxSub score greater than 0.8, 60 % have a GDT-TS score greater than 85, and 58 % have a GDT-HA score greater than 70. For unkinked helices, our predicted models are also highly consistent with their crystal structure. These results provide strong supports for our assumption that kink formation of TM helices in quasi-equilibrium heating processes is relevant to predicting the structure of TM helices.     

Liquid chromatography/tandem mass spectrometry characterization of oxidized amyloid beta peptides as potential biomarkers of Alzheimer's disease

Alzheimer's disease is characterized by the deposition of senile plaques that consist primarily of amyloid beta peptides. There is substantial evidence that amyloid beta is oxidized in vivo, which has led to the suggestion that oxidative stress is an important mediator of Alzheimer's disease. Metal-catalyzed oxidation can mimic in vivo oxidation of amyloid beta because the metal ion binds to the amino acid residues at the site of oxidation, which then deliver reactive oxygen species to that site. Based on electrospray mass spectrometry, it has been suggested that metal-catalyzed oxidation occurs on histidines-13 and -14. Unfortunately, the amyloid beta peptides provide complex spectra, so it is difficult to definitively characterize the sites of oxidation. Trypsin digestion of both native and oxidized amyloid beta1-16 and amyloid beta1-40 resulted in the formation of tryptic peptides corresponding to amyloid beta6-16, which could be separated by liquid chromatography (LC). Sites of oxidation were then unequivocally characterized as histidine-13 and histidine-14 by LC/tandem mass spectrometric (MS/MS) analysis of the tryptic peptides. The ability to analyze the specific amyloid beta6-16 tryptic fragments derived from full-length amyloid beta peptides will make it possible to determine whether oxidation in vivo occurs at specific histidine residues and/or at other amino acid residues such as methionine-35. Using methodology based on LC/MS/MS it will also be possible to analyze the relative amounts of oxidized peptides and native peptide in cerebrospinal fluid from patients with Alzheimer's disease as biomarkers of oxidative stress.     

Replica exchange Monte-Carlo simulations of helix bundle membrane proteins: rotational parameters of helices

We propose a united-residue model of membrane proteins to investigate the structures of helix bundle membrane proteins (HBMPs) using coarse-grained (CG) replica exchange Monte-Carlo (REMC) simulations. To demonstrate the method, it is used to identify the ground state of HBMPs in a CG model, including bacteriorhodopsin (BR), halorhodopsin (HR), and their subdomains. The rotational parameters of transmembrane helices (TMHs) are extracted directly from the simulations, which can be compared with their experimental measurements from site-directed dichroism. In particular, the effects of amphiphilic interaction among the surfaces of TMHs on the rotational angles of helices are discussed. The proposed CG model gives a reasonably good structure prediction of HBMPs, as well as a clear physical picture for the packing, tilting, orientation, and rotation of TMHs. The root mean square deviation (RMSD) in coordinates of C_α atoms of the ground state CG structure from the X-ray structure is 5.03 Å for BR and 6.70 Å for HR. The final structure of HBMPs is obtained from the all-atom molecular dynamics simulations by refining the predicted CG structure, whose RMSD is 4.38 Å for BR and 5.70 Å for HR.     

H spin system identifications of S-sulfonated insulin B chain with 2D-NMR

Resonance assignments of the 1H spectrum of insulin are the basis on which to investigate its solution conformation by using NMR method. Owing to the complicated aggregation behaviour of the molecule to give broadened n. m. r. lines, only limited resonance assignments have been reported. S-sulfonated A and B chains of insulin gave 1H spectra with good resolutions. Based on the 500 MHz absolute 2D-COSY spectrum and 400 MHz phase sensitive DQF-COSY, Relayed-COSY and NOESY spectra of B chain recorded in D2O, all of the spin system identifications of the non-labile protons in the S-sulfonated B chain of insulin were reported including the specific resonance assignments of eight residues: B3Asn, B9Ser, B16Tyr, B22Arg, B26Tyr, B27Thr, B28Pro and B29Lys. The pK values of B16 and B26 tyrosine are 10.65 and 10.60 respectively from pH titration.     

Investigation of the interaction between human hemoglobin and five antioxidants by fluorescence spectroscopy and molecular modeling

L-ascorbic acid, α-tocopherol, procyanidin B3, β-carotene, and astaxanthin are five classic dietary antioxidants. In this study, the interaction between the five antioxidants and human hemoglobin (HHb) was investigated by fluorescence spectroscopy and molecular modeling. The quenching mechanisms of HHb by the five antioxidants are all static quenching. The downward curvature of the Stern–Volmer plots for HHb–procyanidin B3 system at higher concentrations of procyanidin B3 come from the reason for the variation in the number of accessible tryptophan (Trp) residues toward HHb. The upward curvature of the Stern–Volmer plots for HHb–β-carotene system at higher concentrations of β-carotene predominantly by the “sphere of action” quenching mechanism. The binding constants of HHb with the five antioxidants are in the following order as: astaxanthin > L-ascorbic acid > β-carotene > α-tocopherol > procyanidin B3 at 298 K. The binding processes of the five antioxidants to HHb are all entropy process. Thermodynamic analysis and molecular modeling suggest that the hydrophobic forces are the main interaction force in the binding of the five antioxidants to HHb and hydrogen bond interactions between HHb and L-ascorbic acid/α-tocopherol/procyanidin B3/astaxanthin should be also considered. The fluorescence experimental results are in agreement with the results obtained by molecular modeling study.