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 P4₁2₁2 or its enantiomorph P4₃2₁2 with unit-cell axes a = b = 90.9 and c = 82.4 Å. The packing parameter (Matthews parameter) V_m of 2.48 Å³ Da^-1 is consistent with one trimer per asymmetric unit and non-crystallographic threefold symmetry has been confirmed by calculating a selfrotation function. The crystals diffract X-rays to at least 2.3 Å resolution, are stable in an X-ray beam and are therefore appropriate for structure determination. Native data to 2.3 Å 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.