STRUCTURE DETERMINATION OF OPPA AT 2.3-ANGSTROM RESOLUTION USING MULTIPLE-WAVELENGTH ANOMALOUS-DISPERSION METHODS

OppA is a 58.8 kDa bacterial transport protein involved in the transpo rt of peptides across the cytoplasmic membrane of Gram-negative bacter ia. It binds peptides from two to five residues in length but with lit tle sequence specificity. OppA from Salmonella typhimurium has been cl ones and expressed in E. coli and the protein cocrystallized with uran yl acetate, producing two distinct crystal forms with different uraniu m sites. Multiple-wavelength data collected about the uranium L(III) e dge have been collected at the Daresbury Synchrotron Radiation Source (SRS) to a nominal resolution limit of 2.3 Angstrom. Maximum-likelihoo d phasing methods have been used in phase determination from the multi ple-wavelength data giving a readily interpretable electron-density ma p, without any density modification. The electron-density map, calcula ted at 2.3 Angstrom resolution shows OppA to be a bilobal, principally beta-stranded, three-domain protein. The tri-lysine ligand molecule c an be clearly seen in the peptide-binding site between the two lobes.