A large compressibility change of protein induced by a single amino acid substitution

The adiabatic compressibility (beta s) was determined, by means of the precise sound velocity and density measurements, for a series of single amino acid substituted mutant enzymes of Escherichia coli dihydrofolate reductase (DHFR) and aspartate aminotransferase (AspAT). Interestingly, the beta s values of both DHFR and AspAT were influenced markedly by the mutations at glycine-121 and valine-39, respectively, in which the magnitude of the change was proportional to the enzyme activity. This result demonstrates that the local change of the primary structure plays an important role in atomic packing and protein dynamics, which leads to the modified stability and enzymatic function. This is the first report on the compressibility of mutant proteins.