Crystal Structure of the Metallo-beta-Lactamase GOB in the periplasmic di-Zinc form reveals an unusual metal site

LISA, M N; A.M. VIALE; A. J. VILA; LARRIEUX N; MORENO, DM; MORAN BARRIO, J; DRUSIN; BUSCHIAZZO, A.

ANTIMICROBIAL AGENTS AND CHEMOTHERAPY

AMER SOC MICROBIOLOGY

Lugar: Washington; Año: 2016 vol. 60 p. 6013 - 6022

0066-4804

Metallo-beta-lactamases (MBLs) are broad spectrum, Zn(II) dependent lactamases able to confer resistance to virtually every β-lactam antibiotic currently available. The large diversity of active site structures and metal content among MBLs from different sources has limited the design of a pan-MBL inhibitor. GOB-18 is a divergent MBL from subclass B3, expressed by the opportunistic Gram-negative pathogen Elizabethkingia meningoseptica. This MBL is atypical since several residues conserved in B3 enzymes (such as a metal ligand His) are substituted in GOB enzymes. Here we report the crystal structure of the periplasmic di-Zn(II) form of GOB-18. This enzyme displays a unique active site structure, with residue Gln116 coordinating the Zn1 ion through its terminal amide moiety, replacing a ubiquitous His residue. This situation contrasts with that of B2 MBLs, where an equivalent His116Asn substitution leads to a di-Zn(II) inactive species. Instead, both the mono- and di-Zn(II) forms of GOB-18 are active against penicillins, cephalosporins and carbapenems. In silico docking and molecular dynamics simulations indicate that residue Met221 is not involved in substrate binding, in contrast with Ser221, otherwise conserved in most B3 enzymes. These distinctive features are conserved in recently reported GOB orthologues in environmental bacteria. These findings provide valuable information for inhibitor design, and also posit that GOB enzymes might have alternative functions.