Protein-water interactions in a dynamic world

A Statistical Analysis of the Sequence and Structure of Thermophilic and Non-Thermophilic Proteins

Thermophilic proteins have various practical applications in theoretical research and in industry. In recent years, the demand for thermophilic proteins on an industrial scale has been increasing; therefore, the engineering of thermophilic proteins has become a hot direction in the field of protein engineering. However, the exact mechanism of thermostability of proteins is not yet known, for engineering thermophilic proteins knowing the basis of thermostability is necessary. In order to understand the basis of the thermostability in proteins, we have made a statistical analysis of the sequences, secondary structures, hydrogen bonds, salt bridges, DHA (Donor-Hydrogen-Accepter) angles, and bond lengths of ten pairs of thermophilic proteins and their non-thermophilic orthologous. Our findings suggest that polar amino acids contribute to thermostability in proteins by forming hydrogen bonds and salt bridges which provide resistance against protein denaturation. Short bond length and a wider DHA angle provide greater bond stability in thermophilic proteins. Moreover, the increased frequency of aromatic amino acids in thermophilic proteins contributes to thermal stability by forming more aromatic interactions. Additionally, the coil, helix, and loop in the secondary structure also contribute to thermostability.

Measurement of Secondary Structure Changes in Poly-L-lysine and Lysozyme during Acoustically Levitated Single Droplet Drying Experiments by In Situ Raman Spectroscopy

Drying processes such as spray drying, as commonly used in the pharmaceutical industry to convert protein-based drugs into their particulate form, can lead to an irreversible loss of protein activity caused by protein secondary structure changes. Due to the nature of these processes (high droplet number, short drying time), an in situ investigation of the structural changes occurring during a real drying process is hardly possible. Therefore, an approach for the in situ investigation of the expected secondary structural changes during single droplet protein drying in an acoustic levitator by time-resolved Raman spectroscopy was developed and is demonstrated in this paper. For that purpose, a self-developed NIR–Raman sensor generates and detects the Raman signal from the levitated solution droplet. A mathematical spectral reconstruction by multiple Voigt functions is used to quantify the relative secondary structure changes occurring during the drying process. With the developed setup, it was possible to detect and quantify the relative secondary structure changes occurring during single droplet drying experiments for the two chosen model substances: poly-L-lysine, a homopolypeptide widely used as a protein mimic, and lysozyme. Throughout drying, an increase in the β-sheet structure and a decrease in the other two structural elements, α-helix, and random coil, could be identified. In addition, it was observed that the degree of structural changes increased with increasing temperature.

Engineering enhanced thermostability into the Geobacillus pallidus nitrile hydratase

Nitrile hydratases (NHases) are important biocatalysts for the enzymatic conversion of nitriles to industrially-important amides such as acrylamide and nicotinamide. Although thermostability in this enzyme class is generally low, there is not sufficient understanding of its basis for rational enzyme design. The gene expressing the Co-type NHase from the moderate thermophile, Geobacillus pallidus RAPc8 (NRRL B-59396), was subjected to random mutagenesis. Four mutants were selected that were 3 to 15-fold more thermostable than the wild-type NHase, resulting in a 3.4–7.6 ​kJ/mol increase in the activation energy of thermal inactivation at 63 ​°C. High resolution X-ray crystal structures (1.15–1.80 ​Å) were obtained of the wild-type and four mutant enzymes. Mutant 9E, with a resolution of 1.15 ​Å, is the highest resolution crystal structure obtained for a nitrile hydratase to date. Structural comparisons between the wild-type and mutant enzymes illustrated the importance of salt bridges and hydrogen bonds in enhancing NHase thermostability. These additional interactions variously improved thermostability by increased intra- and inter-subunit interactions, preventing cooperative unfolding of α-helices and stabilising loop regions. Some hydrogen bonds were mediated via a water molecule, specifically highlighting the significance of structured water molecules in protein thermostability. Although knowledge of the mutant structures makes it possible to rationalize their behaviour, it would have been challenging to predict in advance that these mutants would be stabilising.

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Random mutagenesis yields a 15-fold increase in nitrile hydratase thermostability.

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Salt bridges and hydrogen bonds improves nitrile hydratase thermostability.

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Water-mediated hydrogen bonds improves protein thermostability.

Contributions of higher-order proximal distribution functions to solvent structure around proteins

The proximal distribution function (pDF) quantifies the probability of finding a solvent molecule in the vicinity of solutes. The approach constitutes a hierarchically organized theory for constructing approximate solvation structures around solutes. Given the assumption of universality of atom cluster-specific solvation, reconstruction of the solvent distribution around arbitrary molecules provides a computationally convenient route to solvation thermodynamics. Previously, such solvent reconstructions usually considered the contribution of the nearest-neighbor distribution only. We extend the pDF reconstruction algorithm to terms including next-nearest-neighbor contribution. As a test, small molecules (alanine and butane) are examined. The analysis is then extended to include the protein myoglobin in the P6 crystal unit cell. Molecular dynamics simulations are performed, and solvent density distributions around the solute molecules are compared with the results from different pDF reconstruction models. It is shown that the next-nearest-neighbor modification significantly improves the reconstruction of the solvent number density distribution in concave regions and between solute molecules. The probability densities are then used to calculate the solute-solvent non-bonded interaction energies including van der Waals and electrostatic, which are found to be in good agreement with the simulated values.

Metabolic limits on classical information processing by biological cells

Biological information processing is generally assumed to be classical. Measured cellular energy budgets of both prokaryotes and eukaryotes, however, fall orders of magnitude short of the power required to maintain classical states of protein conformation and localization at the Å, fs scales predicted by single-molecule decoherence calculations and assumed by classical molecular dynamics models. We suggest that decoherence is limited to the immediate surroundings of the cell membrane and of intercompartmental boundaries within the cell, and that bulk cellular biochemistry implements quantum information processing. Detection of Bell-inequality violations in responses to perturbation of recently-separated sister cells would provide a sensitive test of this prediction. If it is correct, modeling both intra- and intercellular communication requires quantum theory.

Residue interaction networks of K-Ras protein with water molecules identifies the potential role of switch II and P-loop

The mutant K-Ras with aberrant signaling is the primary cause of several cancers. The proposed study investigated the influence of water molecules in K-Ras crystal structure, where they have a significant function by understanding their residue interaction networks (RINs). We analyzed the RINs of K-Ras with and without water molecules and determined their interaction properties. RINs were developed with the help of StructureViz2 and RINspector; further, the changes in K-Ras backbone flexibility were predicted with the DynaMine. We found that the residues K42, I142, and L159 are the hotspots from water, including the K-Ras-GTP complex with the highest residue centrality analysis (RCA) Z-score. The DynaMine prediction calculated the NMR S² value for the frequently mutated positions G12, G13, and Q61 showing a minor shift in flexibility, which make up the P-Loop and switch II of the K-Ras protein. This flexibility shift can account for changes in conformational activity and the protein's GTPase activity, making it difficult to recognize by the effectors and exchange factors. Taken together, our study helps in understanding the functional importance of the water molecules in K-Ras protein and the impact of mutation that modulate the conformational state of the protein.

Probing n-Octyl α-d-Glycosides Using Deuterated Water in the Lyotropic Phase by Deuterium NMR

The lyotropic phase behavior of four common and easily accessible glycosides, n-octyl α-d-glycosides, namely, α-Glc-OC₈, α-Man-OC₈, α-Gal-OC₈, and α-Xyl-OC₈, was investigated. The presence of normal hexagonal (H_I), bicontinuous cubic (V_I), and lamellar (L_α) phases in α-Glc-OC₈ and α-Man-OC₈ including their phase diagrams in water reported previously was verified by deuterium nuclear magnetic resonance (²H NMR), via monitoring the D₂O spectra. Additionally, the partial binary phase diagrams and the liquid crystal structures formed by α-Gal-OC₈ and α-Xyl-OC₈ in D₂O were constructed and confirmed using small- and wide-angle X-ray scattering and ²H NMR. The average number of bound water molecules (n_b) per headgroup in the L_α phase was determined by the systematic measurement of the quadrupolar splitting of D₂O over a wide range of molar ratio values (glycoside/D₂O), especially at high glucoside composition. The number of bound water molecules bound to the headgroup was found to be around 1.5-2.0 for glucoside, mannoside, and galactoside, all of which possesses four OH groups. In the case of xyloside, which has only three OH groups, the bound water content is ∼2.0. Our findings confirmed that the bound water content of all n-octyl α-d-glycosides studied is lower compared to the number of possible hydrogen bonding sites possibly due to the fact that most of the OH groups are involved in intralayer interaction that holds the lipid assembly together.

Unravelling the microhydration frameworks of prototype PAH by infrared spectroscopy: naphthalene–(water)1–3

Microhydration structures of the prototypical PAH, naphthalene, are probed by IR spectroscopy in helium droplets. The sequential water addition produces an extended hydrogen-bonded hydration network bound via π hydrogen bond to the aromatic ring.

Decoupling between the translation and rotation of water in the proximity of a protein molecule

The interaction between water and biomacromolecules is of fundamental interest in biophysics, biochemistry and physical chemistry. By combining neutron scattering and molecular dynamics simulations on a perdeuterated protein at a series of hydration levels, we demonstrated that the translational motion of water is slowed down more significantly than its rotation, when water molecules approach the protein molecule. Further analysis of the simulation trajectories reveals that the observed decoupling results from the fact that the translational motion of water is more correlated over space and more retarded by the charged/polar residues and spatial confinement on the protein surface, than the rotation. Moreover, around the stable protein residues (with smaller atomic fluctuations), water exhibits more decoupled dynamics, indicating a connection between the observed translation-rotation decoupling in hydration water and the local stability of the protein molecule.

In silico modelling and characterization of eight blast resistance proteins in resistant and susceptible rice cultivars

Background

Nucleotide-binding site-leucine-rich repeat (NBS-LRR) resistance genes are the largest class of plant resistance genes which play an important role in the plant defense response. These genes are better conserved than others and function as a recognition-based immune system in plants through their encoded proteins.

Results

Here, we report the effect of Magnaporthe oryzae, the rice blast pathogen inoculation in resistant BR2655 and susceptible HR12 rice cultivars. Transcriptomic profiling was carried out to analyze differential gene expression in these two cultivars. A total of eight NBS-LRR uncharacterized resistance proteins (RP1, RP2, RP3, RP4, RP5, RP6, RP7, and RP8) were selected in these two cultivars for in silico modeling. Modeller 9.22 and SWISS-MODEL servers were used for the homology modeling of eight RPs. ProFunc server was utilized for the prediction of secondary structure and function. The CDvist Web server and Interpro scan server detected the motif and domains in eight RPs. Ramachandran plot of eight RPs confirmed that the modeled structures occupied favorable positions.

Conclusions

From the present study, computational analysis of these eight RPs may afford insights into their role, function, and valuable resource for studying the intricate details of the plant defense mechanism. Furthermore, the identification of resistance proteins is useful for the development of molecular markers linked to resistance genes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-020-00076-0.

Automated orientation of water molecules in neutron crystallographic structures of proteins

The structure and function of proteins are strongly affected by the surrounding solvent water, for example through hydrogen bonds and the hydrophobic effect. These interactions depend not only on the position, but also on the orientation, of the water molecules around the protein. Therefore, it is often vital to know the detailed orientations of the surrounding ordered water molecules. Such information can be obtained by neutron crystallography. However, it is tedious and time-consuming to determine the correct orientation of every water molecule in a structure (there are typically several hundred of them), which is presently performed by manual evaluation. Here, a method has been developed that reliably automates the orientation of a water molecules in a simple and relatively fast way. Firstly, a quantitative quality measure, the real-space correlation coefficient, was selected, together with a threshold that allows the identification of water molecules that are oriented. Secondly, the refinement procedure was optimized by varying the refinement method and parameters, thus finding settings that yielded the best results in terms of time and performance. It turned out to be favourable to employ only the neutron data and a fixed protein structure when reorienting the water molecules. Thirdly, a method has been developed that identifies and reorients inadequately oriented water molecules systematically and automatically. The method has been tested on three proteins, galectin-3C, rubredoxin and inorganic pyrophosphatase, and it is shown that it yields improved orientations of the water molecules for all three proteins in a shorter time than manual model building. It also led to an increased number of hydrogen bonds involving water molecules for all proteins.

Development of a structure-analysis pipeline using multiple-solvent crystal structures of barrier-to-autointegration factor

The multiple-solvent crystal structure (MSCS) approach uses high concentrations of organic solvents to characterize the interactions and effects of solvents on proteins. Here, the method has been further developed and an MSCS data-handling pipeline is presented that uses the Detection of Related Solvent Positions (DRoP) program to improve data quality. DRoP is used to selectively model conserved water molecules, so that an advanced stage of structural refinement is reached quickly. This allows the placement of organic molecules more accurately and convergence on high-quality maps and structures. This pipeline was applied to the chromatin-associated protein barrier-to-autointegration factor (BAF), resulting in structural models with better than average statistics. DRoP and Phenix Structure Comparison were used to characterize the data sets and to identify a binding site that overlaps with the interaction site of BAF with emerin. The conserved water-mediated networks identified by DRoP suggested a mechanism by which water molecules are used to drive the binding of DNA. Normalized and differential B-factor analysis is shown to be a valuable tool to characterize the effects of specific solvents on defined regions of BAF. Specific solvents are identified that cause stabilization of functionally important regions of the protein. This work presents tools and a standardized approach for the analysis and comprehension of MSCS data sets.

Determination of protein-ligand binding modes using fast multi-dimensional NMR with hyperpolarization

Elucidation of small molecule-protein interactions provides essential information for understanding biological processes such as cellular signaling, as well as for rational drug development. Here, multi-dimensional NMR with sensitivity enhancement by dissolution dynamic nuclear polarization (D-DNP) is shown to allow the determination of the binding epitope of folic acid when complexed with the target dihydrofolate reductase. Protein signals are selectively enhanced by polarization transfer from the hyperpolarized ligand. A pseudo three-dimensional data acquisition with ligand-side Hadamard encoding results in protein-side [13C, 1H] chemical shift correlations that contain intermolecular nuclear Overhauser effect (NOE) information. A scoring function based on this data is used to select pre-docked ligand poses. The top five poses are within 0.76 Å root-mean-square deviation from a reference structure for the encoded five protons, showing improvements compared with the poses selected by an energy-based scoring function without experimental inputs. The sensitivity enhancement provided by the D-DNP combined with multi-dimensional NMR increases the speed and potentially the selectivity of structure elucidation of ligand binding epitopes.

Microhydration of protonated biomolecular building blocks: protonated pyrimidine

Protonation and hydration of biomolecules govern their structure, conformation, and function. Herein, we explore the microhydration structure in mass-selected protonated pyrimidine-water clusters (H⁺Pym-W_n, n = 1-4) by a combination of infrared photodissociation spectroscopy (IRPD) between 2450 and 3900 cm^-1 and density functional theory (DFT) calculations at the dispersion-corrected B3LYP-D3/aug-cc-pVTZ level. We further present the IR spectrum of H⁺Pym-N₂ to evaluate the effect of solvent polarity on the intrinsic molecular parameters of H⁺Pym. Our combined spectroscopic and computational approach unequivocally shows that protonation of Pym occurs at one of the two equivalent basic ring N atoms and that the ligands in H⁺Pym-L (L = N₂ or W) preferentially form linear H-bonds to the resulting acidic NH group. Successive addition of water ligands results in the formation of a H-bonded solvent network which increasingly weakens the NH group. Despite substantial activation of the N-H bond upon microhydration, no intracluster proton transfer occurs up to n = 4 because of the balance of relative proton affinities of Pym and W_n and the involved solvation energies. Comparison to neutral Pym-W_n clusters reveals the drastic effects of protonation on microhydration with respect to both structure and interaction strength.

New Insight into Mechanisms of Protein Adaptation to High Temperatures: A Comparative Molecular Dynamics Simulation Study of Thermophilic and Mesophilic Subtilisin-Like Serine Proteases

In high-temperature environments, thermophilic proteins must possess enhanced thermal stability in order to maintain their normal biological functions. However, the physicochemical basis of the structural stability of thermophilic proteins at high temperatures remains elusive. In this study, we performed comparative molecular dynamics simulations on thermophilic serine protease (THM) and its homologous mesophilic counterpart (PRK). The comparative analyses of dynamic structural and geometrical properties suggested that THM adopted a more compact conformation and exhibited more intramolecular interactions and lower global flexibility than PRK, which could be in favor of its thermal stability in high-temperature environments. Comparison between protein solvent interactions and the hydrophobicity of these two forms of serine proteases showed that THM had more burial of nonpolar areas, and less protein solvent hydrogen bonds (HBs), indicating that solvent entropy maximization and mobility may play a significant role in THM's adaption to high temperature environments. The constructed funnel-like free energy landscape (FEL) revealed that, in comparison to PRK, THM had a relatively flat and narrow free energy surface, and a lower minimum free energy level, suggesting that the thermophilic form had lower conformational diversity and flexibility. Combining the FEL theory and our simulation results, we conclude that the solvent (entropy force) plays a significant role in protein adaption at high temperatures.

Water in Ras Superfamily Evolution

The Ras GTPase superfamily of proteins coordinates a diverse set of cellular outcomes, including cell morphology, vesicle transport, and cell proliferation. Primary amino acid sequence analysis has identified Specificity determinant positions (SDPs) that drive diversified functions specific to the Ras, Rho, Rab, and Arf subfamilies (Rojas et al. 2012, J Cell Biol 196:189-201). The inclusion of water molecules in structural and functional adaptation is likely to be a major response to the selection pressures that drive evolution, yet hydration patterns are not included in phylogenetic analysis. This article shows that conserved crystallographic water molecules coevolved with SDP residues in the differentiation of proteins within the Ras superfamily of small GTPases. The patterns of water conservation between protein subfamilies parallel those of sequence-based evolutionary trees. Thus, hydration patterns have the potential to help elucidate functional significance in the evolution of amino acid residues observed in phylogenetic analysis of homologous proteins. © 2019 Wiley Periodicals, Inc.

Water structure in solution and crystal molecular dynamics simulations compared to protein crystal structures

The function of proteins is influenced not only by the atomic structure but also by the detailed structure of the solvent surrounding it. Computational studies of protein structure also critically depend on the water structure around the protein. Herein we compare the water structure obtained from molecular dynamics (MD) simulations of galectin-3 in complex with two ligands to crystallographic water molecules observed in the corresponding crystal structures. We computed MD trajectories both in a water box, which mimics a protein in solution, and in a crystallographic unit cell, which mimics a protein in a crystal. The calculations were compared to crystal structures obtained at both cryogenic and room temperature. Two types of analyses of the MD simulations were performed. First, the positions of the crystallographic water molecules were compared to peaks in the MD density after alignment of the protein in each snapshot. The results of this analysis indicate that all simulations reproduce the crystallographic water structure rather poorly. However, if we define the crystallographic water sites based on their distances to nearby protein atoms and follow these sites throughout the simulations, the MD simulations reproduce the crystallographic water sites much better. This shows that the failure of MD simulations to reproduce the water structure around proteins in crystal structures observed both in this and previous studies is caused by the problem of identifying water sites for a flexible and dynamic protein (traditionally done by overlaying the structures). Our local clustering approach solves the problem and shows that the MD simulations reasonably reproduce the water structure observed in crystals. Furthermore, analysis of the crystal MD simulations indicates a few water molecules that are close to unmodeled electron density peaks in the crystal structures, suggesting that crystal MD could be used as a complementary tool for identifying and modelling water in protein crystallography.

Molecular dynamics simulations can reproduce the water structure around proteins in crystal structure only if a local clustering is performed.

Simultaneous Enhancement of Thermostability and Catalytic Activity of a Metagenome-Derived β-Glucosidase Using Directed Evolution for the Biosynthesis of Butyl Glucoside

Butyl glucoside synthesis using bioenzymatic methods at high temperatures has gained increasing interest. Protein engineering using directed evolution of a metagenome-derived β-glucosidase of Bgl1D was performed to identify enzymes with improved activity and thermostability. An interesting mutant Bgl1D187 protein containing five amino acid substitutions (S28T, Y37H, D44E, R91G, and L115N), showed catalytic efficiency (k_cat/K_m of 561.72 mM⁻¹ s⁻¹) toward ρ-nitrophenyl-β-d-glucopyranoside (ρNPG) that increased by 23-fold, half-life of inactivation by 10-fold, and further retained transglycosidation activity at 50 °C as compared with the wild-type Bgl1D protein. Site-directed mutagenesis also revealed that Asp44 residue was essential to β-glucosidase activity of Bgl1D. This study improved our understanding of the key amino acids of the novel β-glucosidases and presented a raw material with enhanced catalytic activity and thermostability for the synthesis of butyl glucosides.

The role of hydration effects in 5-fluorouridine binding to SOD1: insight from a new 3D-RISM-KH based protocol for including structural water in docking simulations

Misfolded Cu/Zn superoxide dismutase enzyme (SOD1) shows prion-like propagation in neuronal cells leading to neurotoxic aggregates that are implicated in amyotrophic lateral sclerosis (ALS). Tryptophan-32 (W32) in SOD1 is part of a potential site for templated conversion of wild type SOD1. This W32 binding site is located on a convex, solvent exposed surface of the SOD1 suggesting that hydration effects can play an important role in ligand recognition and binding. A recent X-ray crystal structure has revealed that 5-Fluorouridine (5-FUrd) binds at the W32 binding site and can act as a pharmacophore scaffold for the development of anti-ALS drugs. In this study, a new protocol is developed to account for structural (non-displaceable) water molecules in docking simulations and successfully applied to predict the correct docked conformation binding modes of 5-FUrd at the W32 binding site. The docked configuration is within 0.58 Å (RMSD) of the observed configuration. The docking protocol involved calculating a hydration structure around SOD1 using molecular theory of solvation (3D-RISM-KH, 3D-Reference Interaction Site Model-Kovalenko-Hirata) whereby, non-displaceable water molecules are identified for docking simulations. This protocol was also used to analyze the hydrated structure of the W32 binding site and to explain the role of solvation in ligand recognition and binding to SOD1. Structural water molecules mediate hydrogen bonds between 5-FUrd and the receptor, and create an environment favoring optimal placement of 5-FUrd in the W32 binding site.

Analysis of hydration water around human serum albumin using near-infrared spectroscopy

Hydration plays a fundamental role in maintaining the structure and function of proteins. To get a generalized picture of hydrogen bond network of water surrounding human serum albumin (HSA), near-infrared (NIR) spectroscopy was adopted to explore the hydration induced structural changes of water with HSA concentration from 0.015 to 0.746 mmol/L. As HSA concentration increases, there was a nonlinear change in molar extinction coefficients inconsistent with Beer-Lambert law indicating the changes of hydration water induced by HSA and subsequently confirmed by the hydration number. The decreasing of hydration number with HSA concentration was explained by an overlapping hydration layer model. Resolution of the difference spectra with McCabe-Fisher method and aquaphotomics clearly differentiated the hydrogen bonding of hydration water around HSA. A comparison of resolved hydration spectra highlights that free hydrogen bonded water is present in the hydration layer. As the concentration increased, a more ordered hydrogen bonded water network forms around HSA. These measurements provide unique insight into the relationship between the hydration water and HSA, which is important for understanding the dynamics of protein solution in many biochemical processes, and may serve as a basis for the purification in production.

DRoP: Automated detection of conserved solvent-binding sites on proteins

Water and ligand binding play critical roles in the structure and function of proteins, yet their binding sites and significance are difficult to predict a priori. Multiple solvent crystal structures (MSCS) is a method where several X-ray crystal structures are solved, each in a unique solvent environment, with organic molecules that serve as probes of the protein surface for sites evolved to bind ligands, while the first hydration shell is essentially maintained. When superimposed, these structures contain a vast amount of information regarding hot spots of protein-protein or protein-ligand interactions, as well as conserved water-binding sites retained with the change in solvent properties. Optimized mining of this information requires reliable structural data and a consistent, objective analysis tool. Detection of related solvent positions (DRoP) was developed to automatically organize and rank the water or small organic molecule binding sites within a given set of structures. It is a flexible tool that can also be used in conserved water analysis given multiple structures of any protein independent of the MSCS method. The DRoP output is an HTML format list of the solvent sites ordered by conservation rank in its population within the set of structures, along with renumbered and recolored PDB files for visualization and facile analysis. Here, we present a previously unpublished set of MSCS structures of bovine pancreatic ribonuclease A (RNase A) and use it together with published structures to illustrate the capabilities of DRoP.

Biophysical Spandrels form a Hot-Spot for Kosmotropic Mutations in Bacteriophage Thermal Adaptation

Temperature plays a dominating role in protein structure and function, and life has evolved myriad strategies to adapt proteins to environmental thermal stress. Cellular systems can utilize kosmotropic osmolytes, the products of complex biochemical pathways, to act as chemical chaperones. These extrinsic molecules, e.g., trehalose, alter local water structure to modulate the strength of the hydrophobic effect and increase protein stability. In contrast, simpler genetic systems must rely on intrinsic mutation to affect protein stability. In naturally occurring microvirid bacteriophages of the subfamily Bullavirinae, capsid stability is randomly distributed across the phylogeny, suggesting it is not phylogenetically linked and could be altered through adaptive mutation. We hypothesized that these phages could utilize an adaptive mechanism that mimics the stabilizing effects of the kosmotrope trehalose through mutation. Kinetic stability of wild-type ID8, a relative of ΦX174, displays a saturable response to trehalose. Thermal adaptation mutations in ID8 improve capsid stability and reduce responsiveness to trehalose suggesting the mutations move stability closer to the kosmotropic saturation point, mimicking the kosmotropic effect of trehalose. These mutations localize to and modulate the hydrophobicity of a cavern formation at the interface of phage coat and spike proteins-an evolutionary spandrel. Across a series of genetically distinct phages, responsiveness to trehalose correlates positively with cavern hydrophobicity suggesting that the level of hydrophobicity of the cavern may provide a biophysical gating mechanism constraining or permitting adaptation in a lineage-specific manner. Our results demonstrate that a single mutation can exploit pre-existing, non-adaptive structural features to mimic the adaptive effects of complex biochemical pathways.

Heterogeneous Solvation in Distinctive Protein-Protein Interfaces Revealed by Molecular Dynamics Simulations

Water, despite being a driving force in biochemical processes, has an elusively complex microscopic behavior. While water can increase its local density near amphiphilic protein surfaces, water is also thought to evaporate from hydrophobic surfaces and cavities, an effect known as "dewetting". The existence and extent of dewetting effects remains elusive due to the difficulty in observing clear "drying" transitions in experiments or simulations. Here, we use explicit solvent molecular dynamics (MD) simulations to study the molecular solvation at the binding interfaces of two distinctive molecular complexes: the highly hydrophilic barnase-barstar and the highly hydrophobic MDM2-p53. Our simulations, in conjunction with simple volumetric analyses, reveal a strikingly different water behavior at the binding interfaces of these two molecular complexes. In both complexes, we observe significant changes in the water local density as the two proteins approach, supporting the existence of a clear dewetting transition in the case of MDM2-p53, with an onset distance of 5.6-7.6 Å. Furthermore, the solvation analysis reported herein is a valuable tool to capture and quantify persistent or transient dewetting events in future explicit solvent MD simulations.

Field-cycling NMR experiments in an ultra-wide magnetic field range: relaxation and coherent polarization transfer

An experimental method is described allowing fast field-cycling Nuclear Magnetic Resonance (NMR) experiments over a wide range of magnetic fields from 5 nT to 10 T. The method makes use of a hybrid technique: the high field range is covered by positioning the sample in the inhomogeneous stray field of the NMR spectrometer magnet. For fields below 2 mT a magnetic shield is mounted on top of the spectrometer; inside the shield the magnetic field is controlled by a specially designed coil system. This combination allows us to measure T1-relaxation times and nuclear Overhauser effect parameters over the full range in a routine way. For coupled proton-carbon spin systems relaxation with a common T1 is found at low fields, where the spins are "strongly coupled". In some cases, experiments at ultralow fields provide access to heteronuclear long-lived spin states. Efficient coherent polarization transfer is seen for proton-carbon spin systems at ultralow fields as follows from the observation of quantum oscillations in the polarization evolution. Applications to analysis and the manipulation of heteronuclear spin systems are discussed.

Probabilistic analysis for identifying the driving force of protein folding

Toward identifying the driving force of protein folding, energetics was analyzed in water for Trp-cage (20 residues), protein G (56 residues), and ubiquitin (76 residues) at their native (folded) and heat-denatured (unfolded) states. All-atom molecular dynamics simulation was conducted, and the hydration effect was quantified by the solvation free energy. The free-energy calculation was done by employing the solution theory in the energy representation, and it was seen that the sum of the protein intramolecular (structural) energy and the solvation free energy is more favorable for a folded structure than for an unfolded one generated by heat. Probabilistic arguments were then developed to determine which of the electrostatic, van der Waals, and excluded-volume components of the interactions in the protein-water system governs the relative stabilities between the folded and unfolded structures. It was found that the electrostatic interaction does not correspond to the preference order of the two structures. The van der Waals and excluded-volume components were shown, on the other hand, to provide the right order of preference at probabilities of almost unity, and it is argued that a useful modeling of protein folding is possible on the basis of the excluded-volume effect.

Bioactive components and functional properties of biologically activated cereal grains: A bibliographic review

Whole grains provide energy, nutrients, fibers, and bioactive compounds that may synergistically contribute to their protective effects. A wide range of these compounds is affected by germination. While some compounds, such as β-glucans are degraded, others, like antioxidants and total phenolics are increased by means of biological activation of grains. The water and oil absorption capacity as well as emulsion and foaming capacity of biologically activated grains are also improved. Application of biological activation of grains is of emerging interest, which may significantly enhance the nutritional, functional, and bioactive content of grains, as well as improve palatability of grain foods in a natural way. Therefore, biological activation of cereals can be a way to produce food grains enriched with health-promoting compounds and enhanced functional attributes.

Hydrogen Bond Network of Water around Protein Investigated with Terahertz and Infrared Spectroscopy

The dynamical and structural properties of water at protein interfaces were characterized on the basis of the broadband complex dielectric constant (0.25 to 400 THz) of albumin aqueous solutions. Our analysis of the dielectric responses between 0.25 and 12 THz first revealed hydration water with retarded reorientational dynamics extending ∼8.5 Å (corresponding to three to four layers) out from the albumin surface. Second, the number of nonhydrogen-bonded water was decreased in the presence of the albumin solute, indicating protein inhibits the fragmentation of the water hydrogen-bond network. Finally, water molecules at the albumin interface were found to form a distorted hydrogen-bond structure due to topological and energetic disorder of the protein surface. In addition, the intramolecular O-H stretching vibration of water (∼100 THz), which is sensitive to hydrogen-bond environment, pointed to a trend that hydration water has a larger population of strongly hydrogen-bonded water molecules compared with that of bulk water. From these experimental results, we concluded that the "strengthened" water hydrogen bonds at the protein interface dynamically slow down the reorientational motion of water and form the less-defective hydrogen-bond network by inhibiting the fragmentation of water-water hydrogen bonds. Nevertheless, such a strengthened water hydrogen-bond network is composed of heterogeneous hydrogen-bond distances and angles, and thus characterized as structurally "distorted."

Distinct dynamics and interaction patterns in H- and K-Ras oncogenic P-loop mutants

Despite years of study, the structural or dynamical basis for the differential reactivity and oncogenicity of Ras isoforms and mutants remains unclear. In this study, we investigated the effects of amino acid variations on the structure and dynamics of wild type and oncogenic mutants G12D, G12V, and G13D of H- and K-Ras proteins. Based on data from µs-scale molecular dynamics simulations, we show that the overall structure of the proteins remains similar but there are important differences in dynamics and interaction networks. We identified differences in residue interaction patterns around the canonical switch and distal loop regions, and persistent sodium ion binding near the GTP particularly in the G13D mutants. Our results also suggest that different Ras variants have distinct local structural features and interactions with the GTP, variations that have the potential to affect GTP release and hydrolysis. Furthermore, we found that H-Ras proteins and particularly the G12V and G13D variants are significantly more flexible than their K-Ras counterparts. Finally, while most of the simulated proteins sampled the effector-interacting state 2 conformational state, G12V and G13D H-Ras adopted an open switch state 1 conformation that is defective in effector interaction. These differences have implications for Ras GTPase activity, effector or exchange factor binding, dimerization and membrane interaction. Proteins 2017; 85:1618-1632. © 2017 Wiley Periodicals, Inc.

The Roles of Water in the Protein Matrix: A Largely Untapped Resource for Drug Discovery

The value of thoroughly understanding the thermodynamics specific to a drug discovery/design study is well known. Over the past decade, the crucial roles of water molecules in protein structure, function, and dynamics have also become increasingly appreciated. This Perspective explores water in the biological environment by adopting its point of view in such phenomena. The prevailing thermodynamic models of the past, where water was seen largely in terms of an entropic gain after its displacement by a ligand, are now known to be much too simplistic. We adopt a set of terminology that describes water molecules as being "hot" and "cold", which we have defined as being easy and difficult to displace, respectively. The basis of these designations, which involve both enthalpic and entropic water contributions, are explored in several classes of biomolecules and structural motifs. The hallmarks for characterizing water molecules are examined, and computational tools for evaluating water-centric thermodynamics are reviewed. This Perspective's summary features guidelines for exploiting water molecules in drug discovery.

Multifactorial level of extremostability of proteins: can they be exploited for protein engineering?

Research on extremostable proteins has seen immense growth in the past decade owing to their industrial importance. Basic research of attributes related to extreme-stability requires further exploration. Modern mechanistic approaches to engineer such proteins in vitro will have more impact in industrial biotechnology economy. Developing a priori knowledge about the mechanism behind extreme-stability will nurture better understanding of pathways leading to protein molecular evolution and folding. This review is a vivid compilation about all classes of extremostable proteins and the attributes that lead to myriad of adaptations divulged after an extensive study of 6495 articles belonging to extremostable proteins. Along with detailing on the rationale behind extreme-stability of proteins, emphasis has been put on modern approaches that have been utilized to render proteins extremostable by protein engineering. It was understood that each protein shows different approaches to extreme-stability governed by minute differences in their biophysical properties and the milieu in which they exist. Any general rule has not yet been drawn regarding adaptive mechanisms in extreme environments. This review was further instrumental to understand the drawback of the available 14 stabilizing mutation prediction algorithms. Thus, this review lays the foundation to further explore the biophysical pleiotropy of extreme-stable proteins to deduce a global prediction model for predicting the effect of mutations on protein stability.

Molecular motions and free-energy landscape of serine proteinase K in relation to its cold-adaptation: a comparative molecular dynamics simulation study and the underlying mechanisms

The physicochemical bases for enzyme cold-adaptation remain elusive.

Allosteric control of antibody-prion recognition through oxidation of a disulfide bond between the CH and CL chains

Molecular details of the recognition of disordered antigens by their cognate antibodies have not been studied as extensively as folded protein antigens and much is still unknown. To follow the conformational changes in the antibody and cross-talk between its subunits and with antigens, we performed molecular dynamics (MD) simulations of the complex of Fab and prion-associated peptide in the apo and bound forms. We observed that the inter-chain disulfide bond in constant domains restrains the conformational changes of Fab, especially the loops in the CH1 domain, resulting in inhibition of the cross-talk between Fab subdomains that thereby may prevent prion peptide binding. We further identified several negative and positive correlations of motions between the peptide and Fab constant domains, which suggested structural cross-talks between the constant domains and the antigen. The cross-talk was influenced by the inter-chain disulfide bond, which reduced the number of paths between them. Importantly, network analysis of the complex and its bound water molecules observed that those water molecules form an integral part of the Fab/peptide complex network and potential allosteric pathways. On-going work focuses on developing strategies aimed to incorporate these new network communications-including the associated water molecules-toward the grand challenge of antibody design.

Diffusion of Hydration Water around Intrinsically Disordered Proteins

Hydration water dynamics around globular proteins have attracted considerable attention in the past decades. This work investigates the hydration water dynamics around partially/fully intrinsically disordered proteins and compares it to that of the globular proteins via molecular dynamics simulations. The translational diffusion of the hydration water is examined by evaluating the mean-square displacement and the velocity autocorrelation function, while the rotational diffusion is probed through the dipole-dipole time correlation function. The results reveal that the translational and rotational motions of water molecules at the surface of intrinsically disordered proteins/regions are less restricted as compared to those around globular proteins/ordered regions, which is reflected in their higher diffusion coefficient and lower orientational relaxation time. The restricted mobility of hydration water in the vicinity of the protein leads to a sublinear diffusion in a heterogeneous interface. A positive correlation between the mean number of hydrogen bonds and the diffusion coefficient of hydration water implies higher mobility of water molecules at the surface of disordered proteins, which is due to their higher number of hydrogen bonds. Enhanced hydration water mobility around disordered proteins/regions is also related to their higher hydration capacity, low hydrophobicity, and increased internal protein motions. Thus, we generalize that the intrinsically disordered proteins/regions are associated with higher hydration water mobility as compared to globular protein/ordered regions, which may help to elucidate their varied functional specificity.

Dynamics and mechanisms of DNA repair by photolyase

Photolyases, a class of flavoproteins, use blue light to repair two types of ultraviolet-induced DNA damage, a cyclobutane pyrimidine dimer (CPD) and a pyrimidine-pyrimidone (6-4) photoproduct (6-4PP). In this perspective, we review the recent progress in the repair dynamics and mechanisms of both types of DNA restoration by photolyases. We first report the spectroscopic characterization of flavin in various redox states and the active-site solvation dynamics in photolyases. We then systematically summarize the detailed repair dynamics of damaged DNA by photolyases and a biomimetic system through resolving all elementary steps on ultrafast timescales, including multiple intermolecular electron- and proton-transfer reactions and bond-breaking and -making processes. We determined the unique electron tunneling pathways, identified the key functional residues and revealed the molecular origin of high repair efficiency, and thus elucidate the molecular mechanisms and repair photocycles at the most fundamental level. We finally conclude that the active sites of photolyases, unlike the aqueous solution for the biomimetic system, provide a unique electrostatic environment and local flexibility and thus a dedicated synergy for all elementary dynamics to maximize the repair efficiency. This repair photomachine is the first enzyme that the entire functional evolution is completely mapped out in real time.

Slow-to-fast transition of hydrogen bond dynamics in acetamide hydration shell formation

The acetamide hydration shell dynamics speeds up in a remarkable way upon increasing the water amount.

Protein folding: understanding the role of water and the low Reynolds number environment as the peptide chain emerges from the ribosome and folds

The mechanism of protein folding during early stages of the process has three determinants. First, moving water molecules obey the rules of low Reynolds number physics without an inertial component. Molecular movement is instantaneous and size insensitive. Proteins emerging from the ribosome move and rotate without an external force if they change shape, forming and propagating helical structures that increases translocational efficiency. Forward motion ceases when the shape change or propelling force ceases. Second, application of quantum field theory to water structure predicts the spontaneous formation of low density coherent units of fixed size that expel dissolved atmospheric gases. Structured water layers with both coherent and non-coherent domains, form a sheath around the new protein. The surface of exposed hydrophobic amino acids is protected from water contact by small nanobubbles of dissolved atmospheric gases, 5 or 6 molecules on average, that vibrate, attracting even widely separated resonating nanobubbles. This force results from quantum effects, appearing only when the system is within and interacts with an oscillating electromagnetic field. The newly recognized quantum force sharply bends the peptide and is part of a dynamic field determining the pathway of protein folding. Third, the force initiating the tertiary folding of proteins arises from twists at the position of each hydrophobic amino acid, that minimizes surface exposure of the hydrophobic amino acids and propagates along the protein. When the total bend reaches 360°, the leading segment of water sheath intersects the trailing segment. This steric self-intersection expels water from overlapping segments of the sheath and by Newton׳s second law moves the polypeptide chain in an opposite direction. Consequently, with very few exceptions that we enumerate and discuss, tertiary structures are absent from proteins without hydrophobic amino acids, which control the early stages of protein folding and the overall shape of protein. Consequently, proteins only adopt a limited number of forms. The formation of quaternary structures is not necessarily prevented by the absence of hydrophobic amino acids.

The blast resistance gene Pi54of cloned from Oryza officinalis interacts with Avr-Pi54 through its novel non-LRR domains

The dominant rice blast resistance gene Pi54 cloned by map-based cloning approach from indica rice cultivar Tetep confers broad spectrum resistance to Magnaporthe oryzae. In this investigation, an orthologue of Pi54 designated as Pi54of was cloned from Oryza officinalis conferring high degree of resistance to M. oryzae and is functionally validated. We have also characterized the Pi54of protein and demonstrate its interaction with AVR-Pi54 protein. The Pi54of encoded ∼43 kDa small and unique cytoplasmic LRR family of disease resistance protein having unique Zinc finger domain overlapped with the leucine rich repeat regions. Pi54of showed Magnaporthe-induced expression. The phylogenetic and western blot analysis confirmed orthologous nature of Pi54 and Pi54of genes, whereas the identity of protein was confirmed through MALDI-TOF analysis. The in silico analysis showed that Pi54of is structurally more stable than other cloned Pi54 proteins. The molecular docking revealed that Pi54of protein interacts with AVR-Pi54 through novel non-LRR domains such as STI1 and RhoGEF. The STI1 and GEF domains which interact with AVR-Pi54 are also components of rice defensome complex. The Pi54of protein showed differential domain specificity while interacting with the AVR protein. Functional complementation revealed that Pi54of transferred in two rice lines belonging to indica and japonica background imparts enhanced resistance against three highly virulent strains of M. oryzae. In this study, for the first time, we demonstrated that a rice blast resistance gene Pi54of cloned from wild species of rice provides high degree of resistance to M. oryzae and might display different molecular mechanism involved in AVRPi54-Pi54of interaction.