Crystal structure and amino acid sequence of Wolinella succinogenes L-asparaginase

The amino acid sequence and tertiary structure of Wolinella succinogenes L-asparaginase were determined, and were compared with the structures of other type-II bacterial L-asparaginases. Each chain of this homotetrameric enzyme consists of 330 residues. The amino acid sequence is 40-50% identical to the sequences of related proteins from other bacterial 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 the substrate specificity. The overall fold of the protein subunit is almost identical to that observed for other L-asparaginases. Two fragments in each subunit, a very highly flexible loop (approximately 20 amino acids) that forms part of the active site, and the N-terminus (two amino acids), are not defined in the structure. The orientation of Thr14, a residue probably involved in the catalytic activity, indicates the absence of ligand in the active-site pocket. The rigid part of the active site, which includes the asparaginase triad Thr93-Lys 166-Asp94, is structurally very highly conserved with equivalent regions found in other type-II bacterial L-asparaginases.