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Crystal Structure of Class A beta-Lactamase Toho-1 G238C mutant
Structural highlights
FunctionBLT1_ECOLX Has strong cefotaxime-hydrolyzing activity. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedPrevious crystallographic structural analysis of extended-spectrum beta-lactamase Toho-1 predicted that the high flexibility of beta-strand B3, the region that contains a conserved KTG motif and forms one wall of the substrate-binding site, could be one of the key features contributing to Toho-1 activity toward third-generation cephalosporins. To investigate whether this possible flexibility really affects the substrate profile of this enzyme, two Toho-1 mutants have been produced, G238C and G238C/G239in, in which the glycine residue at position 238 was replaced with a cysteine and an additional glycine residue was inserted. Our intent was to introduce a disulfide bond between the cysteine residues at positions 69 and 238, and thus to lock the position of beta-strand B3. The results of 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) titration indicated formation of a new disulfide bridge in the G238C mutant, although disulfide bond formation was not confirmed in the G238C/G239in mutant. Kinetic analysis showed that the activity of the G238C mutant decreased drastically against third-generation cephalosporins, while its catalytic efficiency against penicillins and first-generation cephalosporins was almost identical to that of the wild-type enzyme. This result was consistent with the prediction that flexibility in beta-strand B3 was critical for activity against third-generation cephalosporins in Toho-1. Furthermore, we have determined the crystal structure of the G238C mutant enzyme to analyze the structural changes in detail. The structural model clearly shows the introduction of a new disulfide bridge and that there is no appreciable difference between the overall structures of the wild-type enzyme and the G238C mutant, although the introduced disulfide bond slightly influenced the positions of Ser237 on beta-strand B3 and Asn170 on the Omega loop. The results of our kinetic and structural analyses suggest that the flexibility of beta-strand B3, as well as the positions of Ser237 and the Omega loop, is critical for the substrate specificity expansion of Toho-1. An engineered disulfide bond between residues 69 and 238 in extended-spectrum beta-lactamase Toho-1 reduces its activity toward third-generation cephalosporins.,Shimizu-Ibuka A, Matsuzawa H, Sakai H Biochemistry. 2004 Dec 21;43(50):15737-45. PMID:15595829[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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