Biology subjects

Vemparala, S.

Publications and source records attributed to Vemparala, S..

13 recordsLinked to original sources

bioRxiv2026

Dose-Dependent Softening of Bacterial Model Membranes by Structurally Distinct Antimicrobial Peptides: A Coarse-Grained Molecular Dynamics Study

Antimicrobial peptides (AMPs) act at the membrane interface, where they remodel lipid packing defects and redistribute lateral stresses, yet a quantitative, dose-dependent understanding of how they alter membrane mechanical properties remains incomplete. We use coarse-grained MARTINI 3 molecular dynamics simulations to systematically characterize the mechanical and microstructural response of a 70:30 POPE:POPG bilayer to three AMPs spanning distinct structural classes: aedesin (alpha-helical, 2MMM), arenicin-1 (beta-hairpin, 2JSB), and indolicidin (disordered, 1G89). For each peptide we vary the surface loading from one to four peptides per leaflet and extract the bending modulus Kc, the area compressibility modulus KA, peptide localization depth, bilayer thickness, peptide-lipid and peptide-peptide spatial organization, and leaflet-resolved lipid packing defect distributions. All three peptides soften Kc monotonically with loading, but at per-peptide rates that span a threefold range and order systematically by structural class: - 1.39 {+/-} 0.09, - 0.66 {+/-} 0.04, and - 0.44 {+/-} 0.01 kBT per peptide for aedesin, arenicin-1, and indolicidin, respectively. The tilt and twist moduli remain invariant across all conditions, indicating that the perturbation operates selectively on long-wavelength collective deformation modes. KA softens for the two structured peptides but is statistically indistinguishable from the control for indolicidin, a dissociation we trace to a supraphosphate adsorption versus interfacial insertion dichotomy: structured peptides sit above the phosphate plane and act as supraphosphate wedges, while the disordered peptide threads into the interface without coherently displacing lipids. Independent geometric, spatial-organization, and microstructural observables corroborate this framework, with the deep versus shallow defect remodeling asymmetry providing a clean microstructural counterpart to the Kc-KA dichotomy. Acyl chain order parameters resolve the per-lipid splay from the bilayer-averaged response and show that the per-lipid perturbation tracks conformational state rather than peptide length: the two structured peptides impose comparable per-lipid chain disordering despite differing in length, while the disordered peptide imposes far less. These findings establish a quantitative connection between peptide-induced defect remodeling and the elastic response of the bilayer, and suggest a design principle in which conformational restriction maximizes the per-peptide membrane perturbation, motivating experimental tests on stapled-peptide AMP analogs.

biophysics↗

bioRxiv2024

The Role of Negatively Charged Groups in Antimicrobial Cationic Peptide Mimics: Insights into Membrane Interactions

In this study, we explore cationic amphiphilic methacrylate copolymers incorporating both positively charged AEMA and negatively charged PAMA functional groups, focusing on their interactions with bacterial membranes. Aggregation studies reveal that electrostatic interactions drive the formation of stable polymer aggregates, with block copolymers forming micelle-like structures and random copolymers exhibiting a more uniform distribution. These ternary polymers preferentially interact with deep lipid packing defects in bacterial membranes, stabilizing and expanding these defects, while shallow defects remain largely unaffected due to the unfavorable interaction of anionic groups with lipid headgroups. The role of interfacial water is also critical, as hydration layers surrounding anionic groups shield them from electrostatic repulsion, enabling deeper penetration into the membrane. Comparative analyses highlight the advantages of anionic-containing polymers over previously studied polar-containing systems, which predominantly engage shallow defects and exhibit limited structural adaptability near membranes. These findings underscore the role of anionic residues in enabling adaptable AMP conformations, enhanced membrane engagement, and effective disruption mechanisms, providing valuable insights for the design of biomimetic antimicrobial polymers incorporating different functional groups.

biophysics↗

bioRxiv2024

Role of protein-protein interactions on model chromatin organization

The three-dimensional organization of chromatin is influenced by DNA-binding proteins, through specific and non-specific interactions. However, the role of DNA sequence and interaction between binding proteins in influencing chromatin structure is not yet fully understood. By employing a simple polymer-based model of chromatin, that explicitly considers sequence-dependent binding of proteins to DNA and protein-protein interactions, we elucidate a mechanism for chromatin organization. We find that: (1) Tuning of protein-protein interaction and protein concentration is sufficient to either promote or inhibit the compartmentalization of chromatin. (2) The presence of chromatin acts as a nucleating site for the condensation of the proteins at a density lower than in isolated protein systems. (3) The exponents describing the spatial distance between the different parts of the chromatin, and their contact probabilities are strongly influenced by both sequence and the protein-protein attraction. Our findings have the potential application of re-interpreting data obtained from various chromosome conformation capture technologies, thereby laying the groundwork for advancing our understanding of chromatin organization.

biophysics↗

bioRxiv2023

Role of Tyrosine Phosphorylation in PTP-PEST

We study the influence of tyrosine phosphorylation on PTP-PEST, a cytosolic protein tyrosine phosphatase. Utilizing a combination of experimental data and computational modeling, specific tyrosine sites, notably Y64 and Y88, are identified for potential phosphorylation. Phosphorylation at these sites affects loop dynamics near the catalytic site, altering interactions among key residues and modifying the binding pockets size. This, in turn, impacts substrate binding, as indicated by changes in binding energy. Our findings provide insights into the structural and functional consequences of tyrosine phosphorylation on PTP-PEST, enhancing our understanding of its effects on substrate binding and catalytic conformation.

biophysics↗

bioRxiv2023

Correlation between antimicrobial structural classes and membrane partitioning: Role of emerging lipid packing defects

In this study, a combination of bioinformatics and molecular dynamics simulations is employed to investigate the partitioning behavior of different classes of antimicrobial peptides (AMPs) into model membranes. The main objective is to identify any correlations between the structural characteristics of AMPs and their membrane partitioning mechanisms. The simulation results reveal distinct membrane interactions among the various structural classes of AMPs, particularly in relation to the generation and subsequent interaction with lipid packing defects. Notably, AMPs with a structure-less coil conformation generate a higher number of deep and shallow defects, which are larger in size compared to other classes of AMPs. AMPs with helical component demonstrated the deepest insertion into the membrane. On the other hand, AMPs with a significant percentage of beta sheets tend to adsorb onto the membrane surface, suggesting a potentially distinct partitioning mechanism attributed to their structural rigidity. These findings highlight the diverse membrane interactions and partitioning mechanisms exhibited by different structural classes of AMPs.

biophysics↗

bioRxiv2022

Role of lipid packing defects in determining membraneinteractions of antimicrobial polymers

Understanding the emergence and role of lipid packing defects in the detection and subsequent partitioning of antimicrobial agents into bacterial membranes is essential for gaining insights into general antimicrobial mechanisms. Herein, using methacrylate polymers as a model platform, we investigate the effects of inclusion of various functional groups in the biomimetic antimicrobial polymer design on the aspects of lipid packing defects in model bacterial membranes. Two antimicrobial polymers are considered: ternary polymers composed of cationic, hydrophobic and polar moieties and binary polymers with only cationic and hydrophobic moieties. We find that differing modes of insertion of these two polymers lead to different packing defects in the bacterial membrane. While insertion of both binary and ternary polymers leads to an enhanced number of deep defects in the upper leaflet, shallow defects are moderately enhanced upon interaction with ternary polymers only. We provide conclusive evidence that insertion of antimicrobial polymers in bacterial membrane is preceded by sensing of interfacial lipid packing defects. Our simulation results show that the hydrophobic groups are inserted at a single co-localized deep defect site for both binary and ternary polymers. However, the presence of polar groups in the ternary polymers use the shallow defects close to the lipid-water interface, in addition, to insert into the membrane, which leads to a more folded conformation of the ternary polymer in the membrane environment, and hence a different membrane partitioning mechanism compared to the binary polymer, which acquires an amphiphilic conformation.

biophysics↗

bioRxiv2022

In-silico identification of Tyr232 in AMPKα2 as a dephosphorylation site for the protein tyrosine phosphatase PTP-PEST

The AMP-activated protein kinase (AMPK) is known to be activated by the protein tyrosine phosphatase non-receptor type 12 (PTP-PEST) under hypoxic conditions. This activation is mediated by tyrosine dephosphorylation of the AMPK subunit. However, the identity of the phosphotyrosine residues remains unknown. In this study we first predicted the structure of the complex of the AMPK2 subunit and PTP-PEST catalytic domain using bioinformatics tools and further confirm the stability of the complex using molecular dynamics simulations. Evaluation of the protein-protein interfaces indicates that residue Tyr232 is the most likely site of dephosphorylation on AMPK2. In addition, we explored the effect of phosphorylation of PTP-PEST residue Tyr64 on the stability of the complex. The phosphorylation of Tyr64, an interface residue, enhances the stability of the complex via the rearrangement of a network of electrostatic interactions in conjunction with conformational changes in the catalytic WPD loop. Our findings present a plausible structural basis of AMPK regulation mediated by PTP-PEST and shows how phosphorylation of PTP-PEST could be involved in its activation.

biochemistry↗

bioRxiv2021

Phosphorylation of interfacial phosphosite leads to increased binding of Rap-Raf complex

The effect of phosphorylation of a serine residue in the Rap protein, residing at the complex interface of Rap-Raf complex is studied using atomistic molecular dynamics simulations. As the phosphosite of interest (SER39) is buried at the interface of the Rap-Raf complex, phosphorylation of only Rap protein was simulated and then complexed with the RBD of Raf for further analysis of complex stability. Our simulations reveal that the phosophorylation increases the binding of complex through strong electrostatic interactions and changes the charge distribution of the interface significantly. This is manifested as an increase in stable salt-bridge interactions between the Rap and Raf of the complex. Network analysis clearly shows that the phosphorylation of SER39 reorganizes the community network to include the entire region of Raf chain, including, Raf L4 loop potentially affecting downstream signalling.

biophysics↗

bioRxiv2021

Structural insights on the effects of mutation of a charged binding pocket residue on phosphopeptide binding to 14-3-3 ζ Protein

Mutation of an invariant aspartate residue in the binding pocket of 14-3-3{zeta} isoform to alanine dramatically reduced phosphopeptide binding and induced opening of the binding pocket. Here we use extensive molecular dynamics simulations to understand the role of D124 residue in ligand binding. The simulations show that in the absence of phosphopeptide, the D124A mutation leads to binding pocket reorganization including widening up of the binding pocket at the major groove and repositioning of N173, a key residue that interacts with the main chain of phosphopeptide. These structural changes would interfere with the efficient binding of the peptide, corroborating the experimental observations. Both gain and loss of electrostatic interactions in the form of salt bridges strongly indicate a rearrangement of the network of interactions within the binding pocket. Limited proteolysis coupled mass spectrometry (lip-MS) of the apo and holo forms of WT and mutant protein shows a peptide binding helix otherwise buried in the WT protein was particularly accessible to trypsin in the apo form of the mutant protein and the region was mapped to 158-186 amino acid residues of 14-3-3{zeta}). These results further confirm the dynamic nature of D124A mutant. Unlike other basic residues, the invariant D124 facilitates peptide binding by maintaining the geometry of interacting residues and by enforcing the structural integrity of amphipathic pocket.

biophysics↗

bioRxiv2021

Role of Disulfide Bonds in Membrane Partitioning of a Viral Peptide

The importance of disulfide bond in mediating viral peptide entry into host cells is well known. In the present work, we elucidate the role of disulfide (SS) bond in partitioning mechanism of membrane active Hepatitis A Virus-2B (HAV-2B) peptide, which harbours three cysteine residues promoting formation of multiple SS-bonded states. The inclusion of SS-bond not only results in a compact conformation but also induces distorted -helical hairpin geometry in comparison to SS-free state, resulting in reduced hydrophobic exposure. Owing to this, the partitioning of HAV-2B peptide is completely or partly abolished. In a way, the disulfide bond regulates the partitioning of HAV-2B peptide, such that the membrane remodelling effects of this viral peptide are significantly reduced. The current findings may have potential implications in drug designing, targeting the HAV-2B protein by promoting disulfide bond formation within its membrane active region.

biophysics↗

bioRxiv2020

Effect of Cholesterol on Membrane Partitioning Dynamics of Hepatitis A Virus-2B peptide

Understanding the viral peptide detection, partitioning and subsequent host membrane composition-based response is required for gaining insights into viral mechanism. Here, we probe the crucial role of presence of membrane lipid packing defects, depending on the membrane composition, in allowing the viral peptide belonging to C-terminal Hepatitis A Virus-2B (HAV-2B) to detect, attach and subsequently partition into the host cell membrane mimics. We conclusively show that the hydrophobic residues in the viral peptide detect the transiently present lipid packing defects, insert themselves into such defects, form anchor points and facilitate the partitioning of the peptide. We also show that the presence of cholesterol significantly alters such lipid packing defects, both in size and in number, thus mitigating the partitioning of the membrane active viral peptide into cholesterol-rich membranes. These results show differential ways in which presence and absence of cholesterol can alter the permeability of the host membranes to the membrane active viral peptide component of HAV-2B virus, via lipid packing defects, and can possibly be a part of general membrane detection mechanism for the viroporin class of viruses.

biophysics↗

bioRxiv2020

Towards designing globular antimicrobial peptide mimics: role of polar functional groups in biomimetic ternary antimicrobial polymers

Using atomistic molecular dynamics simulations, we study the interaction of ternary methacrylate polymers, composed of charged cationic, hydrophobic and neutral polar groups, with model bacterial membrane. Our simulation data shows that the random ternary polymers can penetrate deep into the membrane interior and partitioning of even a single polymer has a pronounced effect on the membrane structure. Lipid reorganization, on polymer binding, shows a strong affinity of the ternary polymer for anionic POPG lipids and the same is compared with the control case of binary polymers (only cationic and hydrophobic groups). While binary polymers exhibit strong propensity of acquired amphiphilic conformations upon membrane insertion, our results strongly suggest that such amphiphilic conformations are absent in the case of random ternary polymers. The ternary polymers adopt a more folded conformation, staying aligned in the direction of the membrane normal and subsequently penetrating deeper into the membrane interior suggesting a novel membrane partitioning mechanism without amphiphilic conformations. Finally, we also examine the interactions of ternary polymer aggregates with model bacterial membranes, which show that replacing some of the hydrophobic groups by polar groups leads to weakly held ternary aggregates enabling them to undergo rapid partitioning and insertion into membrane interior. Our work thus underscores the role of inclusion of polar groups into the framework of traditional binary biomimetic antimicrobial polymers and suggests different mode of partitioning into bacterial membranes, mimicking antimicrobial mechanism of globular antimicrobial peptides like Defensin.

biophysics↗

bioRxiv2020

Kinetics of charged polymer collapse: effects of additional salt

Extensive molecular dynamics simulations, using simple charged polymer models, have been employed to probe the kinetics and dynamics of early-stage collapse of charged polymers and the effect of additional monovalent salt on such kinetics. The exponents characterizing the coarsening dynamics during such early-collapse stage via finite size scaling for the case of charged polymers are found to be different from the neutral polymers, suggesting that the collapse kinetics of charged polymers are inherently different from that neutral polymers. The kinetics of coarsening of the clusters along the collapsed trajectory also depends significantly on the counterion valency and for higher valency counterions, multiple regimes are observed and unlike the neutral polymer case, the collapse kinetics are a function of charge density along the charged polymer. Inclusion of additional salt affects the kinetics and conformational landscape along the collapse trajectory. Addition of salt increases the value of critical charge density required to initiate collapse for all the counterion valencies, though the effect is more pronounced for monovalent counterion systems. The addition of salt significantly affects the collapse trajectory in the presence of trivalent counterions via promotion of transient long-distance loop structures inducing a parallel and hierarchical local collapsed conformation leading to faster global collapsed states. This may play a role in understanding the fast folding rates of biopolymers such as proteins and RNA from extended state to a collapsed state in the presence of multivalent counterions before reorganizing into a native fold.

biophysics↗