ANALYSES OF THE STABILITY AND FUNCTION OF 3 SURFACE MUTANTS (R82C, K69H, AND L32R) OF THE GENE V-PROTEIN FROM FF-PHAGE BY X-RAY CRYSTALLOGRAPHY

The high-resolution crystal structure of the gene V protein (GVP) from the Ff filamentous phages (M13, fl, fd) has been solved recently for the wild-type and two surface mutant (Y41F and Y41H) proteins, leading to a plausible model for the polymeric GVP-ssDNA complex (Guan Y, Zha ng H, Wang AHJ, 1995, Protein Sci 4:187-197). The model of the complex shows extensive contacts between neighboring dimer GVPs involving ele ctrostatic interactions between the K69 from one and the D79 and R82 f rom the next dimer. In addition, hydrophobic interactions between the amino acids L32 and L44 from one and G23 from the next dimer also cont ribute to the dimer-dimer interactions. Mutations at the L32, K69, and R82 amino acid sites generally destabilize the protein and many of th ese affect the function of the phage. We have studied the structural e ffects of three mutant proteins involving those sites, i.e., L32R, K69 H, and R82C, by X-ray crystallographic analysis at 2.0 Angstrom resolu tion. In L32R GVP, the structural perturbation is localized, whereas i n K69H and R82C GVPs, some long-range effects are also detected in add ition to the local perturbation. We have interpreted the protein stabi lity and the functional properties associated with those mutations in terms of the observed structural perturbations.