CRYSTAL STRUCTURAL ANALYSIS OF THREE SURFACE MUTANTS OF THE GENE V PROTEIN OF M13. ShaoYu Su, YiGui Gao, Howard Robinson, ⁺⁺Hong Zhang, ⁺Thomas C. Terwilliger, Andrew H.-J. Wang, Division of Biophysics & Dept. of Cell Structural Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, ⁺Division of Life Science & Structural Biology, Los Alamos National Laboratory, Los Alamos, NM 87545

The gene V protein (GVP) from the bacteriophage M13 is a single-stranded DNA binding protein which is a homo dimer of 87 amino acids. The high resolution structure of the M13 GVP has recently been determined by the multiwavelength anomalous diffraction method. In addition, the structure of the Y41H mutant has been determined at 1.7 Å resolution. On the basis of the three dimensional structures and the crystal packing interactions of both the wild-type and Y41H GVP, a model has been proposed to explain the cooperative nature of its binding to ssDNA. The model suggests possible involvements of many surface amino acids either in the binding to DNA, or the protein-protein interactions in the GVP-ssDNA complex. In this work, we present the crystal structures of three mutants involving surface amino acids, L32R, K69H and R82C. The hydrophobic L32 residue is converted into a basic arginine, whereas the basic K69 and R82 are converted into somewhat hydrophobic histidine and cysteine respectively. The diffraction data of these three mutants have been collected to 1.9, 2.0 and 2.0 Å, respectively. The structural refinements are in progress and the results will be reported. This work is supported by NIH. ⁺⁺Present address: Howard Hughes Medical Institute The University of Texas Southwestern Medical Center at Dallas 5323 Harry Hines Blvd. Dallas, Texas 75235-9050 USA