Novel fragments of clavulanate observed in the structure of the class A β-lactamase from Bacillus licheniformis BS3.

OBJECTIVES Our aim was to unravel the inactivation pathway of the class A β-lactamase produced by Bacillus licheniformis BS3 (BS3) by clavulanate. METHODS The interaction between clavulanate and BS3 was studied by X-ray crystallography, pre-steady-state kinetics and mass spectrometry. RESULTS The analysis of the X-ray structure of the complex yielded by the reaction between clavulanate and BS3 indicates that the transient inactivated form, namely the cis-trans enamine complex, is hydrolysed to an ethane-imine ester covalently linked to the active site serine and a pentan-3-one-5-ol acid. It is the first time that this mechanism has been observed in an inactivated β-lactamase. Furthermore, the ionic interactions made by the carboxylic group of pentan-3-one-5-ol may provide an understanding of the decarboxylation process of the trans-enamine observed in the non-productive complex observed for the interaction between clavulanate and SHV-1 and Mycobacterium tuberculosis β-lactamase (Mtu). CONCLUSIONS This work provides a comprehensive clavulanate hydrolysis pathway accounting for the observed acyl-enzyme structures of class A β-lactamase/clavulanate adducts.