The enormous diversity of functions necessary to sustain living systems has necessitated the evolution of equally expansive catalogs of unique protein architectures, each individually tailored to fulfill a particular role. Though individual polypeptide chains adopt a striking number of well-defined 3D structures, it is their ability to hierarchically self-assemble into multicomponent complexes which considerably broadens the scope and complexity of their structural and functional capabilities, making them desirable targets for a broad range of applications, including sensing, catalysis, and therapeutics. Clearly, the directed organization of molecular building blocks into synergistic complexes is a powerful tool for fabricating designer materials and nanoscale machines with advanced capabilities. However, general design rules which dictate protein self-assembly across scales remain undetermined, though numerical simulations have furnished predictions based on geometric considerations and relative interaction strengths. Here we present an experimental realization of such a system. Using in-situ atomic force microscopy measurements, we have characterized the surface-templated self-assembly of a square-shaped protein (C98RhuA) at mineral-water interfaces into three distinct crystal morphologies not observed for 2D C98RhuA crystals grown unsupported in solution, including a metastable phase which only persists under specific solution conditions. Furthermore, we can selectively promote the formation of each specific surface-grown crystal morphology by systematically varying solution concentrations of C98RhuA and KCl, and find that crystallization can occur through both classical and non-classical growth mechanisms. Finally, we employ a semi-quantitative thermodynamic analysis of protein-protein and protein-surface interactions to delineate the contributions of each interface to the selected pathways and underlying multidimensional crystallization free-energy landscape, experimentally validating the rich crystallization behaviors predicted by theory from a single building block.

Nucleation pathway selection yields morphologically diverse two-dimensional protein crystals at solid-liquid interfaces

2019 Fall National Meeting

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