Subset of Fluorophores Is Responsible for Radiation Brightening in Viromimetic Particles

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.

Diffusion and molecular partitioning in hierarchically complex virus-like particles

Viruses are diverse infectious agents found in virtually every type of natural environment. Due to the range of conditions in which viruses have evolved, they exhibit a wide range of structure and function which has been exploited for biotechnology. The self-assembly process of virus-like particles (VLPs), derived from structural virus components, allows for the assembly of a hierarchy of materials. Because VLPs are robust in both their assembly and the final product, functionality can be incorporated through design of their building blocks or chemical modification after their synthesis and assembly. In particular, encapsulation of active enzymes inside VLP results in macromolecular concentration approximating that of cells, introducing excluded volume effects on encapsulated cargo which are not present in traditional experiments done on dilute proteins. This work reviews the hierarchical assembly of VLPs, experiments investigating diffusion in VLP systems, and methods for partitioning of chemical species in VLPs as functional biomaterials.

Ultrafast Collective Excited-State Dynamics of a Virus-Supported Fluorophore Antenna

Radiation brightening was recently observed in a multifluorophore-conjugated brome mosaic virus (BMV) particle at room temperature under pulsed excitation. On the basis of its nonlinear dependence on the number of chromophores, the origins of the phenomenon were attributed to a collective relaxation. However, the mechanism remains unknown. We present ultrafast transient absorption and fluorescence spectroscopic studies which shed new light on the collective nature of the relaxation dynamics in such radiation-brightened, multifluorophore particles. Our findings indicate that the emission dynamics is consistent with a superradiance mechanism. The ratio between the rates of competing radiative and nonradiative relaxation pathways depends on the number of chromophores per virus. The findings suggest that small icosahedral virus shells provide a unique biological scaffold for developing nonclassical, deep subwavelength light sources and may open new avenues for the development of photonic probes for medical imaging applications.