Previously we have de-novo designed a triblock polypeptide with a silk-like midblock that has the ability to co-assemble with DNA into rod-shaped particles each encapsulating one DNA molecule. Its design was inspired by the capsid proteins of the Tobacco Mosaic Virus (TMV) and its assembly follows a kinetic model previously developed to account for the growth of TMV particles. We now show that the templated assembly of silk fibrils on DNA by the artificial capsid polypeptide can be considered as “concentration switched” formation of a silk fibril, where the template acts to increase the local polypeptide concentration. We show that such responsive silk fibril formation only occurs very close to a set of critical polypeptide block lengths that separate fibril-forming from non-fibril forming polypeptide designs. We also show how the very simple artificial capsid polypeptide can be used as a testing ground for methods for real-time single particle level tracking of viral capsid assembly. Using optical tweezers combined with confocal scanning laser microscopy we show that when pentamers formed in solution bind to the DNA these form critical nuclei for particle formation. Furthermore, using Acoustic Force Spectroscopy we show that during particle elongation DNA is condensed in steps of 30 nm, which we hypothesize means that that, as the silk fibrils grow, the DNA is being wrapped around the silk core of the artificial virus particles in discrete steps. These results further demonstrate the usefullness of these polypeptide designs as a model for on the one hand switching and templating silk fibril growth, and on the other hand for the assembly pathways of natural virus capsids.<br/>

Templated silk fibril growth of artificial capsid polypeptides

2019 Spring National Meeting

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