Evolving the Beta Roll Domain for Regulated Molecular Recognition
Molecular recognition is ubiquitous in nature. Frequently antibodies are used in technology applications where biomolecular recognition is to be employed, but antibodies have several limitations in these applications, including difficulty in easily removing bound targets. This becomes especially important in the development of biosensors using electrochemical-based signal transduction schemes.
Instead of trying to engineer allosteric control into a molecular recognition molecule, we have started with intrinsically disordered scaffold, the beta roll domain, and we are working to evolve this allosterically regulated scaffold for biomolecular recognition. The naturally existing beta roll subdomain motif consists of tandem repeats of the sequence GGXGXDXUX, where U is an aliphatic amino acid and X is any amino acid. In the presence of calcium, the disordered peptide reversibly transitions to a beta roll spiral structure of two parallel beta sheet faces, where each beta strand has two solvent exposed variable residues.
We have characterized a native beta roll subdomain with various end-capping groups in order to identify a minimal calcium-responsive beta roll unit. We believe that the beta roll faces are suitable binding surfaces and that calcium-induced structure formation can be used as a mechanism to control the formation of the engineered biomolecular recognition interface. The reversibility of the calcium binding suggests that the engineered biomolecular recognition will likewise be reversibly controllable. We have randomized one face of this minimal beta roll unit and we are using directed evolution to identify beta roll peptides with biomolecular recognition capabilities.
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