Structure of cephalosporin acylase in complex with glutaryl-7-aminocephalosporanic acid and glutarate: insight into the basis of its substrate specificity.

BACKGROUND: Semisynthetic cephalosporins are primarily synthesized from 7-aminocephalosporanic acid (7-ACA), which is obtained by environmentally toxic chemical deacylation of cephalosporin C (CPC). Thus, the enzymatic conversion of CPC to 7-ACA by cephalosporin acylase (CA) would be of great interest. However, CAs use glutaryl-7-ACA (GL-7-ACA) as a primary substrate and the enzyme has low turnover rates for CPC.
RESULTS: The binary complex structures of CA with GL-7-ACA and glutarate (the side-chain of GL-7-ACA) show extensive interactions between the glutaryl moiety of GL-7-ACA and the seven residues that form the side-chain pocket. These interactions explain why the D-alpha-aminoadipyl side-chain of CPC yields a poorer substrate than GL-7-ACA.
CONCLUSIONS: This understanding of the nature of substrate specificity may be useful in the design of an enzyme with an improved performance for the conversion of CPC to 7-ACA. Additionally, the catalytic mechanism of the deacylation reaction was revealed by the ligand bound structures.