Phosphate sensitivity of KPC-2: a hidden variable in β-lactamase kinetics

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Beta-lactamases, particularly KPC-2, are key enzymes in bacterial antibiotic resistance.
• Phosphate buffers are commonly used in enzymatic assays but may affect enzyme function.
• The inhibitory effect of phosphate on beta-lactamase activity is often overlooked.

Purpose of the Study:

• To investigate the inhibitory effect of phosphate on KPC-2 beta-lactamase activity.
• To elucidate the mechanism of phosphate inhibition and identify key amino acid residues involved.
• To compare phosphate sensitivity across different beta-lactamase enzymes.

Main Methods:

• Enzyme kinetics assays were performed using KPC-2 beta-lactamase in the presence of varying phosphate concentrations.
• Site-directed mutagenesis was used to substitute threonine 237 with glycine (T237G).
• Structural and kinetic analyses were conducted to understand phosphate binding and its impact on enzyme function.

Main Results:

• Phosphate acts as a competitive inhibitor of KPC-2 beta-lactamase, reducing catalytic efficiency in a concentration-dependent manner.
• Inhibition is mediated by interactions with threonine 237; the T237G mutation abolished this effect.
• CTX-M-14 and TEM-1 beta-lactamases showed minimal phosphate sensitivity, indicating enzyme-specific buffer effects.
• Phosphate binding primarily impairs substrate affinity and can reduce catalytic turnover.

Conclusions:

• Phosphate buffers can significantly inhibit KPC-2 beta-lactamase activity, potentially leading to underestimation of enzyme function and inhibitor potency.
• The findings underscore the importance of enzyme-specific buffer selection in beta-lactamase assays.
• Standardizing assay conditions is crucial for accurate assessment of beta-lactamase activity and antibiotic resistance mechanisms.