Potential Target Site for Inhibitors in MLS_B Antibiotic Resistance

Area of Science:

• Molecular Biology
• Biochemistry
• Antimicrobial Resistance

Background:

• Macrolide-lincosamide-streptogramin B antibiotic resistance is mediated by Erm proteins, posing significant clinical challenges due to high minimal inhibitory concentrations.
• Erm proteins exhibit conserved regions, including the N-terminal end region (NTER), crucial for their function.
• Specific surface-exposed residues (motif X: S64, Q65, F67) in Erms are implicated in methylation activity and substrate interaction.

Purpose of the Study:

• To investigate the role of specific amino acid residues (S64, Q65, F67) within the conserved motif X of Erm proteins in methylation activity.
• To explore the potential of these residues and the adjacent NTER as targets for developing novel Erm inhibitors.
• To understand how mutations at these positions affect Erm function, substrate RNA recognition, and confer antibiotic resistance.

Main Methods:

• Site-directed mutagenesis was employed to generate mutants at positions S64, Q65, and F67 in Erm proteins.
• Methylation activity of wild-type and mutant Erm proteins was assessed both in vivo (cell resistance) and in vitro.
• Analysis of mutant phenotypes, including changes in activity, cofactor stabilization, and potential substrate RNA interaction.

Main Results:

• Mutations at S64 showed varied effects; S64G, S64A, and S64C retained significant methylation activity, conferring resistance.
• Mutations at Q65 (Q65N, Q65E, Q65R, Q65H) completely abolished methyl group transferring activity.
• Mutations at F67 demonstrated sensitivity to side-chain size and charge; reductions in size or introduction of positive charge drastically reduced activity, while increased size also significantly decreased activity.

Conclusions:

• Amino acids S64, Q65, and F67, along with the NTER, are critical for Erm enzymatic activity and substrate recognition.
• The differential effects of mutations highlight the importance of side-chain properties for catalytic function and substrate binding.
• This conserved region presents a promising target for the rational design of specific inhibitors to combat Erm-mediated antibiotic resistance.