Crystallization and preliminary structural studies of lactose-specific enzyme IIA from Lactococcus lactis

Lactose-specific enzyme IIA of the phosphoenol:pyruvate-dependent sugar phosphotransferase system from Lactococcus lactis has been crystallized in phosphate buffer. The crystals belong to space group P4(1)2(1)2 or its enantiomorph P4(3)2(1)2 with unit-cell axes a = b = 90.9 and c = 82.4 A. The packing parameter (Matthews parameter) V(m) of 2.48 A(3) Da(-1) is consistent with one trimer per asymmetric unit and non-crystallographic threefold symmetry has been confirmed by calculating a self-rotation function. The crystals diffract X-rays to at least 2.3 A resolution, are stable in an X-ray beam and are therefore appropriate for structure determination. Native data to 2.3 A resolution have been collected using a MAR image-plate system at a synchrotron source. One isomorphous heavy-atom derivative has been identified and the presence of an isomorphous signal in the data has been confirmed by Patterson methods.