Abstract
Understanding the molecular mechanisms of bacterial antibiotic resistance will help prepare against further emergence of multi-drug resistant strains. MacQ is an enzyme responsible for the multi-drug resistance of Acidovorax sp. strain MR-S7. MacQ has acylase activity against both N-acylhomoserine lactones (AHLs), a class of signalling compounds involved in quorum sensing, and β-lactam antibiotics. Thus, MacQ is crucial as a quencher of quorum sensing as well as in conferring antibiotic resistance in Acidovorax. Here, we report the X-ray structures of MacQ in ligand-free and reaction product complexes. MacQ forms a 170-kDa capsule-shaped molecule via face-to-face interaction with two heterodimers consisting of an α-chain and a β-chain, generated by the self-cleaving activity of a precursor polypeptide. The electron density of the spacer polypeptide in the hollow of the molecule revealed the close orientation of the peptide-bond atoms of Val20SP-Gly21SP to the active-site, implying a role of the residues in substrate binding. In mutational analyses, uncleaved MacQ retained degradation activity against both AHLs and penicillin G. These results provide novel insights into the mechanism of self-cleaving maturation and enzymatic function of N-terminal nucleophile hydrolases.
Highlights
Acidovorax sp. strain MR-S7 is a gram-negative bacterium that was isolated from activated sludge in a treatment system for penicillin G-polluted wastewater[1,2,3]
The precursors of acylhomoserine lactones (AHLs)-acylases and related enzymes are cleaved into three polypeptide chains (α-chain, internal spacer polypeptide (SP), and β-chain) and the catalytically active mature enzymes are generated as a heterodimer consisting of α- and β-chains, with the SP being released[30]
MacQ is an enzyme belonging to the N-terminal nucleophile (Ntn) hydrolase superfamily
Summary
Acidovorax sp. strain MR-S7 is a gram-negative bacterium that was isolated from activated sludge in a treatment system for penicillin G-polluted wastewater[1,2,3]. Several enzymes exhibiting AHL-acylase activity have been reported. The recombinant MacQ protein exhibited bifunctional acylase activity against various ranges of AHLs and against multiple β-lactam antibiotics, including penicillin G, ampicillin, and amoxicillin (Fig. 1)[3]. PAA α-chain α-chain heterodimer with the SP generated by self-cleaving activity of a MacQ precursor single polypeptide chain. The penicillin G/cephalosporin/AHL-acylases are more homologous to MacQ among the Ntn hydrolases. AhlM and KcPGA, exhibit acylase activity against both AHLs and penicillin G31, 44, similar to MacQ. We describe the X-ray crystal structures of the bifunctional quorum-quenching and β-lactam antibiotic-degrading Ntn hydrolase MacQ in ligand-free form and in complex with reaction products, fatty acid, or phenyl acetic acid. The structures revealed that the three distinct polypeptide chains generated by self-cleaving activity assemble into a capsule-like higher oligomeric complex
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
