Dihydrofolate reductase from Neisseria sp

Area of Science:

• Microbiology
• Biochemistry
• Pharmacology

Background:

• Neisseria species exhibit relative nonsusceptibility to trimethoprim, a dihydrofolate reductase inhibitor.
• Trimethoprim's minimal inhibitory concentrations (MICs) for Neisseria gonorrhoeae are significantly higher than for Escherichia coli.

Purpose of the Study:

• To investigate the molecular basis for trimethoprim's reduced efficacy against Neisseria species.
• To compare dihydrofolate reductase from Neisseria species with that of E. coli.

Main Methods:

• Partial purification of dihydrofolate reductase from five Neisseria species and E. coli.
• Comparison of enzyme properties including molecular weight, substrate affinity (K(m)), and inhibitor affinity (K(i)) for trimethoprim.
• Assessment of isoelectric points, pH activity profiles, and cell envelope permeability.

Main Results:

• Neisseria gonorrhoeae dihydrofolate reductase shares similar molecular weight and substrate affinities with E. coli's enzyme.
• The gonococcal enzyme exhibits a 30-fold lower affinity (higher K(i)) for trimethoprim compared to E. coli.
• Enzyme variations were observed across Neisseria species, with N. meningitidis and N. lactamica enzymes resembling N. gonorrhoeae's.

Conclusions:

• The primary reason for Neisseria's nonsusceptibility to trimethoprim is the poor binding affinity of the bacterial dihydrofolate reductase to the drug.
• Altered cell envelope permeability and increased enzyme levels do not significantly contribute to trimethoprim resistance in these organisms.