Structure determination and refinement at 2.44 Å resolution of argininosuccinate lyase from Escherichia coli

Escherichia coli argininosuccinate lyase has been crystallized from a highly concentrated sample of purified recombinant alpha-methylacyl-CoA racemase, in which it occurred as a minor impurity. The structure has been solved using molecular replacement at 2.44 Angstrom resolution. The enzyme is tetrameric, but in this crystal form there is a dimer in the asymmetric unit. The tetramer has four active sites; each active site is constructed from loops of three different subunits. One of these catalytic loops, near residues Ser277 and Ser278, was disordered in previous structures of active lyases, but is very well ordered in this structure in one of the subunits owing to the presence of two phosphate ions in the active-site cavity. The positions of these phosphate ions indicate a plausible mode of binding of the succinate moiety of the substrate in the competent catalytic complex.