Biology subjects

Mondal, J.

Publications and source records attributed to Mondal, J..

6 recordsLinked to original sources

bioRxiv2018

Mapping the Substrate Recognition Pathway in Cytochrome P450

Cytochrome P450s are ubiquitous metalloenzymes involved in the metabolism and detoxification of foreign components via catalysis of the hydroxylation reactions of a vast array of organic substrates. However, despite the breadth of cytochrome P450 mediated reactions, a long-standing question is: How does the substrate, in the first place, access the catalytic center of cytochrome P450? The prevalence of conflicting crystallographic evidences of both closed and open catalytic center in the substrate-free and substrate-bound cytochrome P450 has given rise to a notion of conformational heterogeneity, which makes the plausible mechanism of substrate recognition by cytochrome P450 puzzling from structural point of view. Here we report multi-microsecond-long unbiased molecular dynamics simulations, which are able to capture the spontaneous process of binding of substrate from bulk solvent to the occluded catalytic center of an archetypal system cytochrome P450cam, at an atomistic precision. In all binding trajectories, the substrate enters through a single channel, where it makes its first contact with the protein-surface and subsequently dwells in a highly long-lived intermediate state, before sliding into the catalytic center of P450cam. The simulated substrate-bound pose and crystallographic pose are in excellent agreement. Contrary to the prevalent hypotheses, our results indicate that a large-scale opening of F/G loop of P450cam is not required for passage of substrate to the catalytic center. Rather, we find that a substrate-induced side-chain displacement of Phe87 residue, coupled with a complex array of dynamical interconversions of multiple metastable substrate conformations along the entry channel, drives the substrate recognition in P450cam. By reconciling multiple precedent investigations, this work put forward an unambiguous view of the substrate recognition mechanism in deep buried cavity of cytochrome P450.

biophysics↗

bioRxiv2018

On identifying collective displacements in apo-proteins that reveal eventual binding pathways

Binding of small molecules to proteins often involves large conformational changes in the latter, which open up pathways to the binding site. Observing and pinpointing these rare events in large scale, all-atom, computations of specific protein-ligand complexes, is expensive and to a great extent serendipitous. Further, relevant collective variables which characterise specific binding or un-binding scenarios are still difficult to identify despite the large body of work on the subject. Here, we show that possible primary and secondary binding pathways can be discovered from short simulations of the apo-protein without waiting for an actual binding event to occur. We use a projection formalism, introduced earlier to study deformation in solids, to analyse local atomic displacements into two mutually orthogonal subspaces -- those which are \"affine\" i.e. expressible as a homogeneous deformation of the native structure, and those which are not. The susceptibility to non-affine displacements among the various residues in the apo-protein is then shown to correlate with typical binding pathways and sites crucial for allosteric modifications. We validate our observation with all-atom computations of three proteins, T4-Lysozyme, Src kinase and Cytochrome P450.

biophysics↗

bioRxiv2018

Assessment and Optimization of Collective Variables for Protein Conformational Landscape: GB1 β-hairpin as a Case Study

Collective variables (CV), when chosen judiciously, can play an important role in recognizing rate-limiting processes and rare events in any biomolecular systems. However, high dimensionality and inherent complexities associated with such biochemical systems render the identification of an optimal CV a challenging task, which in turn precludes the elucidation of underlying conformational landscape in sufficient details. In this context, a relevant model system is presented by 16residue, {beta} hairpin of GB1 protein. Despite being the target of numerous theoretical and computational studies for understanding the protein folding, the set of CVs optimally characterizing the conformational landscape of, {beta} hairpin of GB1 protein has remained elusive, resulting in a lack of consensus on its folding mechanism. Here we address this by proposing a pair of optimal CVs which can resolve the underlying free energy landscape of GB1 hairpin quite efficiently. Expressed as a linear combination of a number of traditional CVs, the optimal CV for this system is derived by employing recently introduced Timestructured Independent Component Analysis (TICA) approach on a large number of independent unbiased simulations. By projecting the replica-exchange simulated trajectories along these pair of optimized CVs, the resulting free energy landscape of this system are able to resolve four distinct wellseparated metastable states encompassing the extensive ensembles of folded,unfolded and molten globule states. Importantly, the optimized CVs were found to be capable of automatically recovering a novel partial helical state of this protein, without needing to explicitly invoke helicity as a constituent CV. Furthermore, a quantitative sensitivity analysis of each constituent in the optimized CV provided key insights on the relative contributions of the constituent CVs in the overall free energy landscapes. Finally, the kinetic pathways con necting these metastable states, constructed using a Markov State Model, provide an optimum description of underlying folding mechanism of the peptide. Taken together, this work oers a quantitatively robust approach towards comprehensive mapping of the underlying folding landscape of a quintessential model system along its optimized collective variables.

biophysics↗

bioRxiv2018

Heterogeneous Impacts of Protein-Stabilizing Osmolytes on Hydrophobic Interaction

Osmolytes mechanism of protecting proteins against denaturation is a longstanding puzzle, further complicated by the complex diversities inherent in protein sequences. An emergent approach in understanding osmolytes mechanism of action towards biopolymer has been to investigate osmolytes interplay with hydrophobic interaction, the major driving force of protein folding. However, the crucial question is whether all these protein-stabilizing osmolytes display a single unified mechanism towards hydrophobic interactions. By simulating the hydrophobic collapse of a macromolecule in aqueous solutions of two such osmoprotectants, Glycine and Trimethyl N-oxide (TMAO), both of which are known to stabilize proteins folded conformation, we here demonstrate that these two osmolytes can impart mutually contrasting effects towards hydrophobic interaction. While TMAO preserves its protectant nature across diverse range of polymer-osmolyte interactions, glycine is found to display an interesting cross-over from being a protectant at weaker polymer-osmolyte interaction to a denaturant of hydrophobicity at stronger polymer-osmolyte interactions. A preferential-interaction analysis reveals that a subtle balance of conformation-dependent exclusion/binding of osmolyte molecules from/to the macromolecule holds the key to overall heterogenous behavior. Specifically, TMAOs consistent stabilization of collapsed configuration of macromolecule is found to be a result of TMAOs preferential binding to polymer via hydrophobic methyl groups. However, polar Glycines cross-over from being a protectant to denaturant across polymer-osmolyte interaction is rooted in its switch from preferential exclusion to preferential binding to the polymer with increasing interaction. Overall, by highlighting the complex interplay of osmolytes with hydrophobic interaction, this work puts forward the necessity of quantitative categorization of osmolytes action in protein.

biophysics↗

bioRxiv2018

An Atomistic view of Short-chain Antimicrobial Biomimetic peptides in Action

Amphiphilic {beta}-peptides, which are rationally designed synthetic oligomers, are established biomimetic alternatives of natural antimicrobial peptides. The ability of these biomimetic peptides to form helical amphiphilic conformation using small number of residues provides a greater synthetic advantage over the naturally occurring antimicrobial peptides, which is reflected in more potent antimicrobial activity of {beta}-peptides than its naturally occurring counterparts. Here we address whether the distinct molecular architecture of short-chain and rigid synthetic peptides compared to relatively long and flexible natural antimicrobial peptides translates to a distinct mechanistic action with membrane. By simulating the interaction of membrane with antimicrobial 10-residue {beta}-peptides at diverse range of concentrations we reveal spontaneous insertion of {beta}-peptides in the membrane interface at a low concentration and occurrence of partial water leakage in the membrane at a high concentration. Intriguingly, unlike prototypical natural antimicrobial peptides, the water molecules leaked inside the membrane by these biomimetic peptides do not span entire membrane, as supported by free energy analysis. As a major advancement, this work brings into lights the key distinction in the membrane-activity of short synthetic biomimetic oligomers relative to the natural long-chain antimicrobial peptides.

biochemistry↗

bioRxiv2018

Atomic Resolution Mechanism of Ligand Binding to a Solvent Inaccessible Cavity in T4 Lysozyme

Ligand binding sites in proteins are often localized to deeply buried cavities, inaccessible to bulk solvent. Yet, in many cases binding of cognate ligands occurs rapidly. An intriguing system is presented by the L99A cavity mutant of T4 Lysozyme (L99A T4L) that rapidly binds benzene (~106 M-1 s-1). Although the protein has long served as a model system for protein thermodynamics and crystal structures of both free and benzene-bound L99A T4L are available, the kinetic pathways by which benzene reaches its solvent-inaccessible binding cavity remain elusive. The current work, using extensive molecular dynamics simulation, achieves this by capturing the complete process of spontaneous recognition of benzene by L99A T4L at atomistic resolution. A series of multi-microsecond unbiased molecular dynamics simulation trajectories unequivocally reveal how benzene, starting in bulk solvent, diffuses to the protein and spontaneously reaches the solvent inaccessible cavity of L99A T4L. The simulated and high-resolution X-ray derived bound structures are in excellent agreement. A robust four-state Markov model, developed using cumulative 60 {micro}s trajectories, identifies and quantifies multiple ligand binding pathways with low activation barriers. Interestingly, none of these identified binding pathways required large conformational changes for ligand access to the buried cavity. Rather, these involve transient but crucial opening of a channel to the cavity via subtle displacements in the positions of key helices (helix4/helix6, helix7/helix9) leading to rapid binding. Free energy simulations further elucidate that these channel-opening events would have been unfavorable in otherwise ligand-inactive wild type T4L. Taken together, by integrating experiments, these simulations provide unprecedented mechanistic insights into complete ligand recognition process in a buried cavity. By illustrating the power of subtle helix movements in opening up multiple pathways for ligand access, this work offers an alternate view of ligand recognition mechanism in a solvent-inaccessible cavity, contrary to common perception of single dominant pathway for ligand binding.

biophysics↗