Desk-top analysis of the structural stability of various point mutations introduced into ribonuclease H.

The structural stability of Escherichia coli ribonuclease HI mutants was analyzed by a pseudo-energy potential developed for evaluating structure-sequence compatibility. From the structure profile, the energy changes of the folding of mutant proteins relative to that of the wild-type, which correspond to the changes of free energy differences, were estimated. They are weakly but significantly correlated with the experimentally determined changes in the melting temperature between the mutant proteins and the wild-type. The correlation coefficient between the experimental data and the computation, estimated for all the known data (96 point mutations) and for the buried site data (32 point mutations), are -0.51 and -0.68, respectively. Experimentally known mechanisms to increase the structural stability are explained by the method: the main contributor to the stability in mutations of Val74 to either Ile or Leu is the side-chain packing energy, and that of Lys95 to Gly is the local conformational energy. This analysis is easy to do on a desk-top computer, and allows one to consider all the sites of possible candidates for point mutations. From the profile, new promising sites to increase the structural stability are suggested.