Protein Engineering vol. 16 no. 11 pp. 831-840, 2003
© 2003 Oxford University Press
Effect of mutations involving charged residues on the stability of staphylococcal nuclease: a continuum electrostatics study
Laboratorium für Physikalische Chemie, ETH Hönggerberg, HCI, CH-8093 Zürich, Switzerland
1 To whom correspondence should be addressed. e-mail: phil{at}igc.phys.chem.ethz.ch
A continuum electrostatics model is used to calculate the relative stabilities of 117 mutants of staphylococcal nuclease (SNase) involving the mutation of a charged residue to an uncharged residue. The calculations are based on the crystallographic structure of the wild-type protein and attempt to take implicitly into account the effect of the mutations in the denatured state by assuming a linear relationship between the free energy changes caused by the mutation in the native and denatured states. A good correlation (linear correlation coefficient of 
0.8) is found with published experimental relative stabilities of these mutants. The results suggest that in the case of SNase (i) charged residues contribute to the stability of the native state mainly through electrostatic interactions, and (ii) native-like electrostatic interactions may persist in the denatured state. The continuum electrostatics method is only moderately sensitive to model parameters and leads to quasi-predictive results for the relative mutant stabilities (error of 2–3 kJ mol–1 or of the order of kBT), except for mutants in which a charged residue is mutated to glycine.
Received March 24, 2003; revised August 11, 2003; accepted September 12, 2003.