Broad spectrum antibiotic-degrading metalloβ-lactamases are phylogenetically diverse Dear Editor,

Enhancement of antibiotic-activity through complexation with metal ionsCombined ITC, NMR, enzymatic and biological studies,

The structural diversity in metallo-β-lactamases (MBLs), especially in the vicinity of the active site, has been a major hurdle in the development of clinically effective inhibitors. Representatives from three variants of the B3 MBL subclass, containing either the canonical HHH/DHH active site motif (present in the majority of MBLs in this subclass) or the QHH/DHH (B3-Q) or HRH/DQK (B3-RQK) variations were reported previously. Here, we describe the structure and kinetic properties of the first example (SIE-1) of a fourth variant containing the EHH/DHH active site motif (B3-E). SIE-1 was identified in the hexachlorocyclohexane-degrading bacterium Sphingobium indicum , and kinetic analyses demonstrate that although it is active against a wide range of antibiotics its efficiency is lower than that of other B3 MBLs, but with improved efficiency towards cephalosporins relative to other β-lactam substrates. The overall fold of SIE-1 is characteristic of the MBLs; the notable variation is observed in the Zn1 site due to the replacement of the canonical His116 by a glutamate. The unusual preference of SIE-1 for cephalosporins and its occurrence in a widespread environmental organism suggests scope for increased MBL-mediated β-lactam resistance. It is thus relevant to include SIE-1 into MBL inhibitor design studies to widen the therapeutic scope of much needed anti-resistance drugs.

No abstract

Genes that confer antibiotic resistance can rapidly be disseminated from one microorganism to another by mobile genetic elements, thus transferring resistance to previously susceptible bacterial strains. the misuse of antibiotics in health care and agriculture has provided a powerful evolutionary pressure to accelerate the spread of resistance genes, including those encoding β-lactamases. These are enzymes that are highly efficient in inactivating most of the commonly used β-lactam antibiotics. However, genes that confer antibiotic resistance are not only associated with pathogenic microorganisms, but are also found in non-pathogenic (i.e. environmental) microorganisms. Two recent examples are metal-dependent β-lactamases (MBLs) from the marine organisms Novosphingobium pentaromativorans and Simiduia agarivorans. previous studies have demonstrated that their β-lactamase activity is comparable to those of well-known MBLs from pathogenic sources (e.g. NDM-1, AIM-1) but that they also possess efficient lactonase activity, an activity associated with quorum sensing. Here, we probed the structure and mechanism of these two enzymes using crystallographic, spectroscopic and fast kinetics techniques. Despite highly conserved active sites both enzymes demonstrate significant variations in their reaction mechanisms, highlighting both the extraordinary ability of MBLs to adapt to changing environmental conditions and the rather promiscuous acceptance of diverse substrates by these enzymes. Antibiotic resistance is a rising socioeconomic problem due to the lack of industrial antibiotic development over the last two decades 1,2. Although new antibiotic substances are developed continuously by academic groups, very few are transferred into industrial production and clinical application. Moreover, there is a lack of new (bio) chemical strategies to overcome antibiotic resistance, and although many of the newly developed antibiotic compounds may display novel structural features they mostly act upon the same cellular mechanisms (i.e. inhibition of cell wall biosynthesis, blocking ribosome function or cell replication). Therefore, there is an imminent global threat that available antibiotic substances may not be effective against ever faster evolving microbial pathogens; the most prominent among these pathogens are listed by the WHO and categorised in class 1-3 threat levels 3,4. To meet the societal challenges exerted by these microbial pathogens, new mechanisms to combat antibiotic