Crystallization and preliminary X-ray diffraction studies of the peptide methionine sulfoxide reductase from Escherichia coli

Peptide methionine sulfoxide reductase mediates the reduction of protein su lfoxide methionyl residues back to methionines and could thus be implicated in the antioxidant defence of organisms. Hexagonal crystals of the Escheri chia coli enzyme (MsrA) were obtained by the hanging-drop vapour-diffusion technique. They belong to space group P6(5)22, with unit-cell parameters a = b = 102.5, c = 292.3 Angstrom, gamma = 120 degrees. A native data set was collected at 1.9 Angstrom resolution. Crystals of selenomethionine-substit uted MsrA were also grown under the same crystallization conditions. A thre e-wavelength MAD experiment has led to the elucidation of the positions of the Se atoms and should result in a full structure determination.