Time-resolved beta-lactam cleavage by L1 metallo-beta-lactamase

Serial x-ray crystallography can uncover binding events, and subsequent chemical conversions occurring during enzymatic reaction. Here, we reveal the structure, binding and cleavage of moxalactam antibiotic bound to L1 metallo-beta-lactamase (MBL) from Stenotrophomonas maltophilia. Using time-resolved serial synchrotron crystallography, we show the time course of beta-lactam hydrolysis and determine ten snapshots (20, 40, 60, 80, 100, 150, 300, 500, 2000 and 4000ms) at 2.20 angstrom resolution. The reaction is initiated by laser pulse releasing Zn2+ ions from a UV-labile photocage. Two metal ions bind to the active site, followed by binding of moxalactam and the intact beta-lactam ring is observed for 100ms after photolysis. Cleavage of beta-lactam is detected at 150ms and the ligand is significantly displaced. The reaction product adjusts its conformation reaching steady state at 2000 ms corresponding to the relaxed state of the enzyme. Only small changes are observed in the positions of Zn2+ ions and the active site residues. Mechanistic details captured here can be generalized to other MBLs.