(741d) Modeling the Self-Assembly of Super-Charged Green Fluorescent Proteins

Predicting the self-assembly of complex biological macromolecules presents a formidable theoretical challenge owing to the hierarchy of length and time scales involved. However, the vast size of the genetic sequence space for ordered assembly enables the formation of complex, synthetic materials from otherwise relatively simple building blocks. Here we explore the use of assembly-promoting tunable patches for biomolecular materials by investigating whether supercharging of protein surfaces enables their ordered assembly into terminal and extended structures. Using fluorescent proteins as a model system, we experimentally identify conditions favoring the formation of ~11 nm diameter protomers with internal symmetry that further assemble into micron-scale particles.

Using a novel computational approach based on the combination of approximately hard molecular shape represented by the GFP solvent-excluded surface and screened electrostatic interactions, we rationalize the stability of different candidate complexes, to explain the experimental findings. We find qualitative agreement with experiment for the predicted stability window as a function of added salt, and we are able to identify a unique, stable candidate structure that is consistent with TEM micrographs of the protomer. Our results suggest that supercharging is a versatile strategy to engineer synthetic, hierarchically self-assembled biomaterials, and our combined experimental and computational approach provides a model for investigating the thermodynamics of biomolecular assemblies.