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Publication Abstract from PubMed

BEL-1 is an acquired class A ESBL found in P. aeruginosa clinical isolates from Belgium, which is divergent from other ESBLs (max. identity, 54% with GES-type enzymes). This enzyme is efficiently inhibited by clavulanate, imipenem and moxalactam. Crystals of BEL-1 were obtained at pH 5.6 and the structure of native BEL-1 was determined from orthorhombic and monoclinic crystal forms, at 1.60-A and 1.48 A resolution, respectively. By soaking native BEL-1 crystals, complexes with imipenem (monoclinic form, 1.79 A res.) and moxalactam (orthorhombic form, 1.85 A res.) were also obtained. In the acyl-enzyme complexes, imipenem and moxalactam differ by the position of the alpha-substituent and of the carbonyl oxygen (in or out the oxyanion hole). More surprisingly, the Omega-loop, which includes the catalytically-relevant residue Glu166, was found in different conformations in the various subunits, resulting in the Glu166 side chain to be rotated outwards the active site or even in displacements of its Calpha atom up to approx. 10 A. A BEL-1 variant showing the single Leu162Phe substitution (BEL-2) confers a higher level of resistance to CAZ, CTX and FEP and shows significantly lower KM values as compared to those of BEL-1, especially with oxyiminocephalosporins. BEL-1 Leu162 is located at the beginning of the Omega-loop, and surrounded by Phe72, Leu139, Leu148 and Leu169 (contact distances, 3.8-4.0 A). This small hydrophobic cavity could not reasonably accommodate the bulkier Phe162 found in BEL-2 without altering neighboring residues or the Omega-loop itself, thus likely causing an important alteration of the enzyme kinetic properties.

Crystal Structure of the Pseudomonas aeruginosa BEL-1 Extended-Spectrum beta-Lactamase and its Complex with Moxalactam and Imipenem.,Pozzi C, De Luca F, Benvenuti M, Poirel L, Nordmann P, Rossolini GM, Mangani S, Docquier JD Antimicrob Agents Chemother. 2016 Sep 26. pii: AAC.00936-16. PMID:27671060^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.