Principal Investigator Jonathan King
Though the tailspike lacks disulfide bonds, the protrimer intermediate contains interchain disulfide bonds, which must be reduced to form the native trimer. Each of the eight single Cys>Ser mutant proteins was able to fold and assemble at low temperature, and once folded exhibited wild type thermostability and biological activity. Thus the cysteine thiols make only very limited contributions to the stability and activity of the native state. However, the kinetics of the in vitro refolding of the mutant tailspikes were distinctly altered, indicating that these –SH side chains and S-S bonds play critical kinetic roles in productive folding and assembly at physiological temperatures. We suspect that the transient interchain S-S bonds keep the chains in proper registration in preparation for the wrapping of the chains to form the triple ß-helix. Ryan Simkovsky is investigating the possibility that a thioredoxin motif found in the tailspike sequence is responsible for the disulfide bond chemistry.