A Hierarchical Approach to the Design of Protein Crystals

Abstract

Despite the fact that scientists have been using X-ray crystallography for the structure determination of proteins for nearly 80 years, understanding and controlling the crystallization of proteins has remained an outstanding challenge. In order to help address this challenge, the main focus of my doctoral research has been to design self-assembling protein crystals from the bottom up. Inspired by nature’s ability to create complicated architectures using the hierarchical assembly of symmetric proteins, my goal has been to design symmetrical protein building blocks that crystalize when mixed together in solution into a predefined lattice architecture and without requiring vapor diffusion conditions . Because of the strict mathematical relationship of symmetry elements in crystal space groups, I designed these protein building blocks to assemble in a way that satisfies the geometric constraints of each lattice architecture. In two cases, I was successful in designing amino acid mutations that resulted in the spontaneous self-assembly of protein crystals; however, they both ended up forming unexpected lattice architectures. To address this challenge of off-target assembly, I developed a hierarchical method that consists of custom-making building blocks that are geometrically related to one another. I have experimentally characterized tens of these, and am working on continuing to systematically generate crystal designs from these custom building blocks. This new hierarchical design protocol and its results represent a step towards the accurate design of self-assembling protein crystals by using a hierarchical design approach that leverages recent strides in protein design. Achieving a general method to design self-assembling protein crystals would open the door to a new generation of biomaterials that are genetically programmable and also enable unparalleled nanoscale patterning.