CRYSTAL-STRUCTURE AND AMINO-ACID-SEQUENCE OF WOLINELLA-SUCCINOGENES L-ASPARAGINASE

The amino acid sequence and tertiary structure of Wolinella succinogen es L-asparaginase were determined, and were compared with the structur es of other type-II bacterial L-asparaginases. Each chain of this homo tetrameric enzyme consists of 330 residues. The amino acid sequence is 40-50% identical to the sequences of related proteins from other bact erial sources, and all residues previously shown to be crucial for the catalytic action of these enzymes are identical. Differences between the amino acid sequence of W. succinogenes L-asparaginase and that of related enzymes are discussed in terms of the possible influence on th e substrate specificity. The overall fold of the protein subunit is al most identical to that observed for other L-asparaginases. Two fragmen ts in each subunit, a very highly flexible loop (approximate to 20 ami no acids) that forms part of the active site, and the N-terminus (two amino acids), are not defined in the structure. The orientation of Thr 14, a residue probably involved in the catalytic activity, indicates t he absence of ligand in the active-site pocket. The rigid part of the active site, which includes the asparaginase triad Thr93-Lys166-Asp94, is structurally very highly conserved with equivalent regions found i n other type-II bacterial L-asparaginases.