Purification and crystallization of recombinant Escherichia coli malate dehydrogenase

Malate dehydrogenase from Escherichia coli has been crystallized with polyethylene glycol and citrate buffer at pH 5.7. The enzyme was obtained from an E. coli strain in which the chromosomal malate dehydrogenase gene was contained on a pBR322 vector. Two types of crystals have been observed; a monoclinic C2 form and an orthorhombic C222(1) form, which is found infrequently. Monoclinic crystals were used as seeds in several rounds of crystallization until large crystals suitable for diffraction analysis were available. A complete X-ray data set to 2.0 A has been collected.