Motion of the Zinc Ions in Catalysis by a Dizinc Metallo-β-Lactamase

We report rapid-freeze-quench X-ray absorption spectroscopy of a dizinc metallo-beta-lactamase (MBL) reaction intermediate. The Zn(II) ions in the dinuclear active site of the S. maltophilia Class B3 M beta L move away from each other, by similar to 0.3 angstrom after 10 ms of reaction with nitrocefin, from 3.4 to 3.7 angstrom. Together with our previous characterization of the resting enzyme and its nitrocefin product complex, where the Zn(II) ion separation relaxes to 3.6 angstrom, these data indicate a scissoring motion of the active site that accompanies the ring-opening step. The average Zn(II) coordination number of 4.5 in the resting enzyme appears to be maintained throughout the reaction with nitrocefin. This is the first direct structural information available on early stage dizinc metallo-beta-lactamase catalysis.