Perturbations in inter-domain associations may trigger the onset of pathogenic transformations in PrP(C): insights from atomistic simulations

Insights into the dynamic interactions of RNase a and osmolytes through computational approaches

Osmolytes are small organic molecules that are known to stabilize proteins and other biological macromolecules under various stressful conditions. They belong to various categories such as amino acids, methylamines, and polyols. These substances are commonly known as 'compatible solutes' because they do not disrupt cellular processes and help regulate the osmotic balance within cells. In the case of ribonuclease A (RNase A), which is prone to aggregation, the presence of osmolytes can help to maintain its structural stability and prevent unwanted interactions leading to protein aggregation. In this study, we investigated the interaction between RNase A and several osmolytes using molecular docking and molecular dynamics (MD) simulations. We performed molecular docking to predict the binding mode and binding affinity of each osmolyte with RNase A. MD simulations were then carried out to investigate the dynamics and stability of the RNase A-osmolyte complexes. Our results show that two osmolytes, glucosylglycerol and sucrose have favorable binding affinities with RNase A. The possible role of these osmolytes in stabilizing the RNase A and prevention of aggregation is also explored. By providing computational insights into the interaction between RNase A and osmolytes, the study offers valuable information that could aid in comprehending the mechanisms by which osmolytes protect proteins and help in designing therapeutics for protein-related disorders based on osmolytes. These findings may have significant implications for the development of novel strategies aimed at preventing protein misfolding and aggregation in diverse disease conditions.Communicated by Ramaswamy H. Sarma.

Investigating the novel-binding site of RPA2 on Menin and predicting the effect of point mutation of Menin through protein-protein interactions

Protein-protein interactions (PPIs) play a critical role in all biological processes. Menin is tumor suppressor protein, mutated in multiple endocrine neoplasia type 1 syndrome and has been shown to interact with multiple transcription factors including (RPA2) subunit of replication protein A (RPA). RPA2, heterotrimeric protein required for DNA repair, recombination and replication. However, it's still remains unclear the specific amino acid residues that have been involved in Menin-RPA2 interaction. Thus, accurately predicting the specific amino acid involved in interaction and effects of MEN1 mutations on biological systems is of great interests. The experimental approaches for identifying amino acids in menin-RPA2 interactions are expensive, time-consuming, and challenging. This study leverages computational tools, free energy decomposition and configurational entropy scheme to annotate the menin-RPA2 interaction and effect on menin point mutation, thereby proposing a viable model of menin-RPA2 interaction. The menin-RPA2 interaction pattern was calculated on the basis of different 3D structures of menin and RPA2 complexes, constructed using homology modeling and docking strategy, generating three best-fit models: Model 8 (- 74.89 kJ/mol), Model 28 (- 92.04 kJ/mol) and Model 9 (- 100.4 kJ/mol). The molecular dynamic (MD) was performed for 200 ns and binding free energies and energy decomposition analysis were calculated using Molecular Mechanics Poisson-Boltzmann Surface Area (MM/PBSA) in GROMACS. From binding free energy change, model 8 of Menin-RPA2 exhibited most negative binding energy of - 205.624 kJ/mol, followed by model 28 of Menin-RPA2 with - 177.382 kJ/mol. After S606F point mutation in Menin, increase of BFE (ΔGbind) by - 34.09 kJ/mol in Model 8 of mutant Menin-RPA2 occurs. Interestingly, we found a significant reduction of BFE (ΔGbind) and configurational entropy by - 97.54 kJ/mol and - 2618 kJ/mol in mutant model 28 as compared the o wild type. Collectively, this is the first study to highlight the configurational entropy of protein-protein interactions thereby strengthening the prediction of two significant important interaction sites in menin for the binding of RPA2. These predicted sites could be vulnerable for structural alternation in terms of binding free energy and configurational entropy after missense mutation in menin.

Targeting two potential sites of SARS-CoV-2 main protease through computational drug repurposing

Before the rise of SARS-CoV-2, emergence of different coronaviruses such as SARS-CoV and MERS-CoV has been reported that indicates possibility of the future novel pathogen from the coronavirus family at a pandemic level. In this context, explicit studies on identifying inhibitors focused on the coronavirus life cycle, are immensely important. The main protease is critical for the life cycle of coronaviruses. Majority of the work done on the inhibitor studies on the catalytically active dimeric SARS-CoV-2 main protease (M^pro), primarily focussed on the catalytic site of a single protomer, with a few targeting the dimeric site. In this study, we have exploited the FDA-approved drugs, for a computational drug repurposing study against the M^pro. A virtual screening approach was employed with docking and molecular dynamics (MD) methods. Out of 1576, FDA-approved compounds, our study suggests three compounds: netupitant, paliperidone and vilazodone as possible inhibitors with a potential to inhibit both sites (monomeric and dimeric) of the M^pro. These compounds were found to be stable during the MD simulations and their post simulation binding energies were also correlated for both the targeted sites, suggesting equal binding capacity. This unique efficiency of the reported compounds might support further experimental studies on developing inhibitors against SARS-CoV-2 main protease.Communicated by Ramaswamy H. Sarma.

A molecular twist on hydrophobicity

A thorough exploration of the molecular basis for hydrophobicity with a comprehensive set of theoretical tools and an extensive set of organic solvent S/water binary systems is discussed in this work. Without a single exception, regardless of the nature or structure of S, all quantum descriptors of bonding yield stabilizing S⋯water interactions, therefore, there is no evidence of repulsion and thus no reason for etymological hydrophobicity at the molecular level. Our results provide molecular insight behind the exclusion of S molecules by water, customarily invoked to explain phase separation and the formation of interfaces, in favor of a complex interplay between entropic, enthalpic, and dynamic factors. S⋯water interfaces are not just thin films separating the two phases; instead, they are non-isotropic regions with density gradients for each component whose macroscopic stability is provided by a large number of very weak dihydrogen contacts. We offer a definition of interface as the region in which the density of the components in the A/B binary system is not constant. At a fundamental level, our results contribute to better current understanding of hydrophobicity.

Notwithstanding the very weak nature of individual contacts, it is the cumulative effect of a large number of interactions (green NCI surfaces) which provides macroscopic stability to the interfaces.

Combining molecular dynamics simulations and experimental analyses in protein misfolding

The fold of a protein determines its function and its misfolding can result in loss-of-function defects. In addition, for certain proteins their misfolding can lead to gain-of-function toxicities resulting in protein misfolding diseases such as Alzheimer's, Parkinson's, or the prion diseases. In all of these diseases one or more proteins misfold and aggregate into disease-specific assemblies, often in the form of fibrillar amyloid deposits. Most, if not all, protein misfolding diseases share a fundamental molecular mechanism that governs the misfolding and subsequent aggregation. A wide variety of experimental methods have contributed to our knowledge about misfolded protein aggregates, some of which are briefly described in this review. The misfolding mechanism itself is difficult to investigate, as the necessary timescale and resolution of the misfolding events often lie outside of the observable parameter space. Molecular dynamics simulations fill this gap by virtue of their intrinsic, molecular perspective and the step-by-step iterative process that forms the basis of the simulations. This review focuses on molecular dynamics simulations and how they combine with experimental analyses to provide detailed insights into protein misfolding and the ensuing diseases.

Detecting early stage structural changes in wild type, pathogenic and non-pathogenic prion variants using Markov state model

The conversion of prion protein from normal to scrapie followed by the aggregation and deposition of this scrapie form leads to various neurodegenerative diseases. A few studies carried out by researchers suggest that E219K prion mutant (glutamate to lysine mutation at residue position 219) is more stable than wild type protein. However a similar point mutation E200K (glutamate to lysine mutation at residue position 200) is pathogenic. In this study we have carried out detailed atomistic simulation of the wild type, pathogenic mutant E200K and E219K mutant which provides more stability. The aim of the study was to detect the early structural changes present in all the three variants which might be responsible for the stability or for their conversion from PrPC to PrPSc. MSM based analyses have been carried out to find out the differences between WT, E200K and E219K systems. Markov state model (MSM) analysis was able to predict the intermediate states which helped to understand the effect of same mutation at two different locations. The MSM analysis was able to show that the extra stability of E219K mutant may be a result of the increase in number of native contacts, strong salt bridges and less random motions. While pathogenicity of E200K mutant can be attributed to loss of some crucial salt-bridge interactions, increased random motions between helix 2 and helix 3.

Markov state model to find out the differences between WT, E200K and E219K systems.

Structural insight into the antiprion compound inhibition mechanism of native prion folding over misfolding

Transition of a physiological folded prion (PrP^C ) into a pathogenic misfolded prion (PrP^Sc ) causes lethal neurodegenerative disorders and prion diseases. Antiprion compounds have been developed to prevent this conversion; however, their mechanism of action remains unclear. Recently, we reported two antiprion compounds, BMD29 and BMD35, identified by in silico and in vitro screening. In this study, we used extensive explicit-solvent molecular dynamics simulations to investigate ligand-binding inhibition by antiprion compounds in prion folding over misfolding behavior at acidic pH. The two antiprion compounds and the previously reported GN8 compound resulted in a remarkably stabilized intermediate by binding to the hotspot region of PrP^C , whereas free PrP^C and the inactive compound BMD01 destabilized the structure of PrP^C leading to the misfolded form. The results uncovered a secondary structural transition of free PrP^C and transition suppression by the antiprion compounds. One of the major misfolding processes in PrP^C , alternation of hydrophobic core residues, disruption of intramolecular interactions, and the increase in residue solvent exposure were significantly inhibited by both antiprion compounds. These findings provide insights into prion misfolding and inhibition by antiprion compounds.

Complexes between cationic pyridylphenylene dendrimers and ovine prion protein: do hydrophobic interactions matter?

MD simulation predicted the possible binding sites for the dendrimer interactions with protein while ITC data revealed both electrostatic and hydrophobic driving forces for the complexation.

Interdomain salt-bridges in the Ebola virus protein VP40 and their role in domain association and plasma membrane localization

The Ebola virus protein VP40 is a transformer protein that possesses an extraordinary ability to accomplish multiple functions by transforming into various oligomeric conformations. The disengagement of the C-terminal domain (CTD) from the N-terminal domain (NTD) is a crucial step in the conformational transformations of VP40 from the dimeric form to the hexameric form or octameric ring structure. Here, we use various molecular dynamics (MD) simulations to investigate the dynamics of the VP40 protein and the roles of interdomain interactions that are important for the domain-domain association and dissociation, and report on experimental results of the behavior of mutant variants of VP40. The MD studies find that various salt-bridge interactions modulate the VP40 domain dynamics by providing conformational specificity through interdomain interactions. The MD simulations reveal a novel salt-bridge between D45-K326 when the CTD participates in a latch-like interaction with the NTD. The D45-K326 salt-bridge interaction is proposed to help domain-domain association, whereas the E76-K291 interaction is important for stabilizing the closed-form structure. The effects of the removal of important VP40 salt-bridges on plasma membrane (PM) localization, VP40 oligomerization, and virus like particle (VLP) budding assays were investigated experimentally by live cell imaging using an EGFP-tagged VP40 system. It is found that the mutations K291E and D45K show enhanced PM localization but D45K significantly reduced VLP formation.

Conformational dynamics of a hydrophobic prion fragment (113-127) in different pH and osmolyte solutions

Prion diseases are characterized by a conformational change in prion protein from its native state into beta-sheet rich aggregates that are neurotoxic. The central domain that contain a highly conserved hydrophobic region of the protein play an important role in the toxicity. The conformation of the proteins is largely influenced by various solvent environments. Here we report results of study of hydrophobic prion fragment peptide PrP(113-127) under different pH and osmolytes solution conditions. The secondary structure and the folding of PrP(113-127) was determined using circular dichroism and fluorescence spectroscopic methods. The results indicate that PrP(113-127) adopts a random coil conformation in aqueous buffer at neutral pH and that converted into beta sheet on aging. Even though the initial random coil conformation was similar in different pH conditions, the acidic as well as basic pH conditions delays the conformational transition to beta sheet. FRET results indicate that the distance between N and C-terminal regions increased on aging due to unfolding by self-assembly of the peptide into an organized beta sheet structure. Presence of osmolytes, prevented or decelerated the aggregation process of PrP(113-127) peptide.