Phi-Analysis of CusF: Alanine-Scanning Mutagenesis to Reveal the Folding Transition State
Authors:Claudina Cammack, Sundee Olson, Casey Yarborough
Mentor:Blake Gillespie, Associate Professor of Chemistry, California State University Channel Islands
What are the key interactions of protein structure that govern its folding kinetics? Can the presence of ligand affect this process? We are using the copper chaperone protein CusF as a model system for the exploration of folding pathways, employing a protein engineering strategy in which each amino acid is systematically substituted with alanine. Protein stability and folding kinetics for each mutant are monitored by tryptophan fluorescence, and ‘phi-value’ computed. When a given substitution affects both folded state and folding kinetics similarly, the phi-value is close to 1, and the residue is deemed to be structured in the transition state. In this way, we are building a map of the interactions critical to CusF’s folding reaction. So far, we have mutated some 47% of CusF’s sequence. We report a preliminary analysis of a subset of mutants, and we compare our crude map to the transition states of other proteins.