Structures of two highly homologous bacterial L-­asparaginases: a case of enantiomorphic space groups

Quasi-enantiomorphic crystals of the Y25F mutant of Escherichia coli L-asparaginase and of the native Erwinia chrysanthemi L-asparaginase were obtained in the hexagonal space groups P6₅22 and P6₁22, respectively. The structures of these highly homologous enzymes were solved by molecular replacement and were refined with data extending to 2.2-2.5 Å. These structures were compared with each other, as well as with other L-asparaginase structures previously observed with different crystal packing. It is concluded that the observed phenomenon, which is rare, was most likely to have arisen by chance.