A Triple Mutant in the Ω-loop of TEM-1 β-Lactamase Changes the Substrate Profile via a Large Conformational Change and an Altered General Base for Catalysis

• Published in: The Journal of biological chemistry 2015-04, Vol.290 (16), p.10382-10394
• Main Authors: Stojanoski, Vlatko, Chow, Dar-Chone, Hu, Liya, Sankaran, Banumathi, Gilbert, Hiram F., Prasad, B. V. Venkataram, Palzkill, Timothy
• Format: Article
• Language: English
• Subjects: Antibiotic Resistance; beta-Lactam Resistance - genetics; Beta-Lactamase; beta-Lactamases - chemistry; beta-Lactamases - genetics; beta-Lactamases - metabolism; Biocatalysis; Ceftazidime - chemistry; Ceftazidime - metabolism; Crystallography, X-Ray; Enzyme Catalysis; Enzyme Evolution; Enzyme Kinetics; Enzyme Structure; Escherichia coli - enzymology; Escherichia coli - genetics; Gene Expression; Glutamic Acid - chemistry; Glutamic Acid - metabolism; Hydrogen-Ion Concentration; Kinetics; Models, Molecular; Mutation; Penicillins - chemistry; Penicillins - metabolism; Protein Stability; Protein Structure; Protein Structure and Folding; Protein Structure, Secondary; Protein Structure, Tertiary; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Structure-Activity Relationship; Substrate Specificity; Tyrosine - chemistry; Tyrosine - metabolism; X-ray Crystallography
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M114.633438

β-Lactamases are bacterial enzymes that hydrolyze β-lactam antibiotics. TEM-1 is a prevalent plasmid-encoded β-lactamase in Gram-negative bacteria that efficiently catalyzes the hydrolysis of penicillins and early cephalosporins but not oxyimino-cephalosporins. A previous random mutagenesis study identified a W165Y/E166Y/P167G triple mutant that displays greatly altered substrate specificity with increased activity for the oxyimino-cephalosporin, ceftazidime, and decreased activity toward all other β-lactams tested. Surprisingly, this mutant lacks the conserved Glu-166 residue critical for enzyme function. Ceftazidime contains a large, bulky side chain that does not fit optimally in the wild-type TEM-1 active site. Therefore, it was hypothesized that the substitutions in the mutant expand the binding site in the enzyme. To investigate structural changes and address whether there is an enlargement in the active site, the crystal structure of the triple mutant was solved to 1.44 Å. The structure reveals a large conformational change of the active site Ω-loop structure to create additional space for the ceftazidime side chain. The position of the hydroxyl group of Tyr-166 and an observed shift in the pH profile of the triple mutant suggests that Tyr-166 participates in the hydrolytic mechanism of the enzyme. These findings indicate that the highly conserved Glu-166 residue can be substituted in the mechanism of serine β-lactamases. The results reveal that the robustness of the overall β-lactamase fold coupled with the plasticity of an active site loop facilitates the evolution of enzyme specificity and mechanism. Background: TEM-1 β-lactamase hydrolyzes penicillins and early cephalosporins but not oxyimino-cephalosporins. Results: A TEM-1 triple mutant, W165Y/E166Y/P167G, exhibits ceftazidime hydrolysis and a large active site conformational change. Conclusion: The mutant has an enlarged active site to accommodate ceftazidime and an alternative catalytic residue, Tyr-166. Significance: The study reveals plasticity in β-lactamase structure and mechanism in the evolution of altered substrate specificity.