A Noncanonical Metal Center Drives the Activity of the Sediminispirochaeta smaragdinae Metallo-beta-lactamase SPS-1.

In an effort to evaluate whether a recently reported putative metallo-β-lactamase (MβL) contains a novel MβL active site, SPS-1 from Sediminispirochaeta smaragdinae was overexpressed, purified, and characterized using spectroscopic and crystallographic studies. Metal analyses demonstrate that recombinant SPS-1 binds nearly 2 equiv of Zn(II), and steady-state kinetic studies show that the enzyme hydrolyzes carbapenems and certain cephalosporins but not β-lactam substrates with bulky substituents at the 6/7 position. Spectroscopic studies of Co(II)-substituted SPS-1 suggest a novel metal center in SPS-1, with a reduced level of spin coupling between the metal ions and a novel Zn1 metal binding site. This site was confirmed with a crystal structure of the enzyme. The structure shows a Zn2 site that is similar to that in NDM-1 and other subclass B1 MβLs; however, the Zn1 metal ion is coordinated by two histidine residues and a water molecule, which is held in position by a hydrogen bond network. The Zn1 metal...