6dja | pdb_00006dja
ZN-DEPENDENT 5/B/6 METALLO-BETA-LACTAMASE FROM BACILLUS CEREUS
Structural highlights
Function[BLAB_BACCE] Confers resistance to the different beta-lactams antibiotics (penicillin, cephalosporin and carbapenem) via the hydrolysis of the beta-lactam ring. Benzylpenicillin is a better substrate than cephalosporin C and ampicillin (PubMed:3131315, PubMed:2501295).[1] [2] [3] Publication Abstract from PubMedThe hydrolysis of beta-lactam antibiotics by beta-lactamase enzymes is the most prominent antibiotic resistance mechanism for many pathogenic bacteria. Out of this broad class of enzymes, metallo-beta-lactamases are of special clinical interest because of their broad substrate specificities. Several in vitro inhibitors for various metallo-beta-lactamases have been reported with no clinical efficacy. Previously, we described a 10-nucleotide single stranded DNA aptamer (10-mer) that inhibits Bacillus cereus 5/B/6 metallo-beta-lactamase very effectively. Here, we find that the aptamer shows uncompetitive inhibition of Bacillus cereus 5/B/6 metallo-beta-lactamase during cefuroxime hydrolysis. To understand the mechanism of inhibition, we report a 2.5 A resolution X-ray crystal structure and solution-state NMR analysis of the free enzyme. Chemical shift perturbations were observed in the HSQC spectra for several residues upon titrating with increasing concentrations of the 10-mer. In the X-ray crystal structure, these residues are distal to the active site, suggesting an allosteric mechanism for the aptamer inhibition of the enzyme. HADDOCK molecular docking simulations suggest that the 10-mer docks 26 A from the active site. We then mutated the three lysine residues in the basic binding patch to glutamine and measured the catalytic activity and inhibition by the 10-mer. No significant inhibition of these mutants was observed by the 10-mer as compared to wild type. Interestingly, mutation of Lys50 (Lys78; according to standard MBL numbering system) resulted in reduced enzymatic activity relative to wild type in the absence of inhibitor, further highlighting an allosteric mechanism for inhibition. A DNA aptamer reveals an allosteric site for inhibition in metallo-beta-lactamases.,Khan NH, Bui AA, Xiao Y, Sutton RB, Shaw RW, Wylie BJ, Latham MP PLoS One. 2019 Apr 22;14(4):e0214440. doi: 10.1371/journal.pone.0214440., eCollection 2019. PMID:31009467[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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