A point mutation leads to altered product specificity in beta-lactamase catalysis

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• Beta-lactamases confer antibiotic resistance by hydrolyzing beta-lactam antibiotics.
• The catalytic mechanism involves a transient acyl-enzyme intermediate.
• Class A beta-lactamases, like that from Bacillus licheniformis, are crucial targets for understanding resistance.

Purpose of the Study:

• To investigate the impact of a specific point mutation (Asn-170 to Leucine) on the catalytic mechanism and product specificity of beta-lactamase.
• To elucidate the consequences of disrupting the deacylation step in the beta-lactamase reaction.

Main Methods:

• Site-directed mutagenesis was used to create the N170L beta-lactamase mutant.
• The mutant enzyme was reacted with penicillins.
• Reaction products were analyzed to determine the altered catalytic pathway and final products.

Main Results:

• The N170L mutation prevented normal hydrolysis, leading to a novel deacylation pathway.
• A thiazolidine-oxazolinone intermediate was formed, which rapidly broke down.
• The final products, N-phenylacetylglycine and N-formylpenicillamine, indicate a shift in enzyme specificity.

Conclusions:

• A single point mutation can fundamentally alter an enzyme's catalytic mechanism and product specificity.
• The N170L mutation transforms beta-lactamase activity towards that of a D-Ala-D-Ala-carboxypeptidase.
• This study provides a novel example of enzyme mechanism reprogramming through targeted mutagenesis.