Biology subjects

Hadden-Perilla, J. A.

Publications and source records attributed to Hadden-Perilla, J. A..

9 recordsLinked to original sources

bioRxiv2026

Toward Robust Characterization of Dynamic Binding Pockets: Lessons from the HBV Capsid Assembly Modulator Site

Protein function often depends on ligand binding pockets that fluctuate among conformational states, altering their size, shape, topology, and accessibility, yet quantitative comparison of these dynamic cavities remains challenging because their boundaries are often inherently ambiguous. The measure volinterior algorithm uses fuzzy-boundary detection to characterize enclosed molecular spaces; here, the hepatitis B virus (HBV) capsid assembly modulator (CAM) binding site is used as a model system to develop and validate a practical workflow for applying the method to dynamic protein binding pockets. The resulting methodology provides practical guidance for parameter selection and evaluation, establishes a standardized protocol for quantitative characterization of the HBV CAM pocket, and demonstrates robust, reproducible performance across conformational ensembles derived from molecular dynamics (MD) simulations. More broadly, this work provides a reproducible strategy for adapting measure volinterior to other dynamic binding pockets, enabling consistent comparison of pocket geometry among independent structural studies. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=105 SRC="FIGDIR/small/743403v1_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@540692org.highwire.dtl.DTLVardef@7b94dborg.highwire.dtl.DTLVardef@169c478org.highwire.dtl.DTLVardef@e1de80_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2026

Modeling Reveals How Direct-Acting Antivirals Redirect HBV Capsid Assembly Pathways to Noninfectious Products

Hepatitis B virus (HBV) infections cause chronic liver disease, resulting in about one million deaths per year, and there is currently no cure. Recent work has shown that a class of small molecules called capsid assembly modulators (CAMs) is promising for treating HBV. CAMs bind to HBV capsid protein subunits and alter their assembly, leading to non-functional and malformed structures rather than functional, closed shells. However, the mechanisms by which CAMs alter capsid assembly pathways remain unclear. Here, we extend a recently-developed kinetic Monte Carlo (KMC) model for HBV capsid assembly to simulate how CAMs affect assembly. In the model, CAMs alter assembly by preferentially binding to interfaces between certain quasi-equivalent subunit conformations. Simulations of the model reproduce experimental assembly product distributions. By analyzing assembly trajectories, we clarify the roles of thermodynamics and kinetics in determining assembly products, identify assembly mechanisms, and predict the key intermediates that lead to either capsids or malformed structures. Our findings enhance our fundamental understanding of capsid assembly, help advance the development of CAMs as a treatment for HBV and, more broadly, inform efforts to direct self-assembly pathways toward specific products.

biophysics↗

bioRxiv2025

Computational biophysical characterization of a superradiant virus-like particle in its ground state

Superradiance (SR) arises when fluorophores radiate collectively rather than independently, producing ultrabright emission bursts. Recent experiments show that dye-labeled virus-like particles (VLPs) can exhibit SR at room temperature, where the VLP scaffold organizes dyes into a macrodipole of coherent emitters under pulsed excitation. To elucidate the biophysical basis of this phenomenon, microsecond-scale all-atom molecular dynamics (MD) simulations were performed on intact Brome mosaic virus (BMV) VLPs, comparing the native scaffold to a capsid decorated with Oregon Green 488 (OG). Results show that OG conjugation at K105 induces only subtle structural changes: a slight expansion of VLP volume and marginally higher inter-subunit flexibility, while overall shell morphology and pore architecture remain intact. However, dianionic OG alters VLP electrostatics, increasing water exchange across the shell and reducing chloride permeability. Dyes bound in pentamers are more closely packed and conformationally restricted than those in hexamers, and their transition dipoles more frequently adopt parallel orientations predicted to favor excitonic coupling and cooperative emission. By examining the role of scaffold architecture in dye interactions and dynamics, this work offers a mechanistic framework and design principles for engineering SR-VLPs as next-generation fluorescent probes and photonic materials.

biophysics↗

bioRxiv2025

All-atom MD simulations of the HPV16 capsid

Human papillomavirus (HPV) type 16, one of over 200 known genotypes, is a major cause of anogenital and oropharyngeal cancers worldwide. The L1 protein capsid - which represents the exterior shell of the virus - plays essential roles in host cell adhesion and entry, and is the major antigen used in vaccines that protect against HPV. Here we report an all-atom molecular dynamics (MD) simulation of the intact capsid in explicit solvent, a calculation comprising 16.8 million atoms. The detailed motions and emergent biophysical properties revealed by this simulation provide critical insights into capsid function and immunogenicity, establishing a new platform for rational drug design and antibody engineering.

biophysics↗

bioRxiv2025

RNA demethylase FTO uses conserved aromatic residues to recognize the mRNA 5' cap and promote efficient m6Am demethylation

The RNA demethylase FTO acts as a methyl eraser to remove either internal N6-methyladenosine (m6A) or 5' end N6-2'-O-dimethyladenosine (m6Am) modifications on mRNA. FTO has an intrinsic preference and significantly faster demethylation rates in vitro for m6Am modifications located at the 5' mRNA cap structure, but the structural basis for FTOs ability to discriminate m6A versus m6Am modifications has remained unknown. Here we utilize molecular dynamics simulations of FTO-RNA cap complexes to identify conserved aromatic residues on the surface of FTO involved in 5 cap recognition. Subsequent mutagenesis and enzymology experiments validate the specificity of these residues in engaging the 5' cap structure to promote m6Am demethylation. We also identify a nonpolar surface on FTO that interacts with the 2'-O-methyl group of m6Am to impact demethylation kinetics. This work provides the first structure-level insights into how FTO selectively catalyzes m6Am versus m6A demethylation on mRNA and advances our understanding of how FTO activity is regulated by diverse mechanisms to help control the epitranscriptome.

biochemistry↗

bioRxiv2023

AMBERff at scale: Multimillion-atom simulations with AMBER force fields in NAMD

All-atom molecular dynamics (MD) simulations are an essential structural biology technique with increasing application to multimillion-atom systems, including viruses and cellular machinery. Classical MD simulations rely on parameter sets, such as the AMBER family of force fields (AMBERff), to accurately describe molecular motion. Here, we present an implementation of AMBERff for use in NAMD that overcomes previous limitations to enable high-performance, massively-parallel simulations encompassing up to two billion atoms. Single-point potential energy comparisons and case studies on model systems demonstrate that the implementation produces results that are as accurate as running AMBERff in its native engine.

biophysics↗

bioRxiv2022

Multiscale Modeling of Hepatitis B Virus Capsid Assembly and its Dimorphism

Hepatitis B Virus (HBV) is an endemic, chronic virus that leads to 800,000 deaths per year. Central to the HBV lifecycle, the viral core has a protein capsid assembled from many copies of a single protein. The capsid protein adopts different (quasi-equivalent) conformations to form icosahedral capsids containing 180 or 240 proteins, T=3 or T=4 respectively in Caspar-Klug nomenclature. HBV capsid assembly has become an important target for new antivirals; nonetheless the assembly pathways and mechanisms that control HBV dimorphism remain unclear. We describe computer simulations of HBV assembly, using a coarse-grained model that has parameters learned from all-atom molecular dynamics simulations of a complete HBV capsid, and yet is computationally tractable. Dynamical simulations with the resulting model reproduce experimental observations of HBV assembly pathways and products. By constructing Markov state models and employing transition path theory, we identify pathways leading to T=3, T=4, and other experimentally observed capsid morphologies. The analysis identifies factors that control this polymorphism, in particular, the conformational free energy landscape of the capsid proteins and their interactions.

biophysics↗

bioRxiv2021

All-Atom MD Simulations of the HBV Capsid Complexed with AT130 Reveal Secondary and Tertiary Structural Changes and Mechanisms of Allostery

The hepatitis B virus (HBV) capsid is an attractive drug target, relevant to combating viral hepatitis as a major public health concern. Among small molecules known to interfere with capsid assembly, the phenylpropenamides, including AT130, represent an important anti-viral paradigm based on disrupting the timing of genome encapsulation. Crystallographic studies of AT130-bound complexes have been essential in explaining the effects of the small molecule on HBV capsid structure; however, computational examination reveals that key changes attributed to AT130 were erroneous, likely a consequence of interpreting poor resolution arising from a highly flexible protein. Here, all-atom molecular dynamics simulations of an intact AT130-bound HBV capsid reveal that, rather than damaging spike helicity, AT130 enhances the capsids ability to recover it. A new conformational state is identified, which can lead to dramatic opening of the intradimer interface and disruption of communication within the spike tip. A novel salt bridge is also discovered, which can mediate contact between the spike tip and fulcrum even in closed conformations, revealing a mechanism of direct communication across these domains. Combined with dynamical network analysis, results describe a connection between the intra- and interdimer interfaces and enable mapping of allostery traversing the entire capsid protein dimer.

biophysics↗

bioRxiv2020

Scalable Analysis of Authentic Viral Envelopeson FRONTERA

Enveloped viruses infect host cells via fusion of their viral envelope with the plasma membrane. Upon cell entry, viruses gain access to all the macromolecular machinery necessary to replicate, assemble, and bud their progeny from the infected cell. By employing molecular dynamics simulations to characterize the dynamical and chemical-physical properties of viral envelopes, researchers can gain insights into key determinants of viral infection and propagation. Here, the Frontera supercomputer is leveraged for large-scale analysis of authentic viral envelopes, whose lipid compositions are complex and realistic. VMD with support for MPI is employed on the massive parallel computer to overcome previous computational limitations and enable investigation into virus biology at an unprecedented scale. The modeling and analysis techniques applied to authentic viral envelopes at two levels of particle resolution are broadly applicable to the study of other viruses, including the novel coronavirus that causes COVID-19. A framework for carrying out scalable analysis of multi-million particle MD simulation trajectories on Frontera is presented, expanding the the utility of the machine in humanity’s ongoing fight against infectious disease.Competing Interest StatementThe authors have declared no competing interest.View Full Text

biophysics↗