Crystallization and preliminary structure determination of the transfer protein TraM from the Gram-positive conjugative plasmid pIP501

The major means of horizontal gene spread (e. g. of antibiotic resistance) is conjugative plasmid transfer. It presents a serious threat especially for hospitalized and immuno-suppressed patients, as it can lead to the accelerated spread of bacteria with multiple antibiotic resistances. Detailed information about the process is available only for bacteria of Gram-negative (G-) origin and little is known about the corresponding mechanisms in Gram-positive (G+) bacteria. Here we present the purification, biophysical characterization, crystallization and preliminary structure determination of the TraM C-terminal domain (TraM Delta, comprising residues 190-322 of the full-length protein), a putative transfer protein from the G+ conjugative model plasmid pIP501. The crystals diffracted to 2.5 angstrom resolution and belonged to space group P1, with unit-cell parameters a = 39.21, b = 54.98, c = 93.47 angstrom, alpha = 89.91, beta = 86.44, gamma = 78.63 degrees and six molecules per asymmetric unit. The preliminary structure was solved by selenomethionine single-wavelength anomalous diffraction.