Exploring mechanisms of mupirocin resistance and hyper-resistance

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Mupirocin is a broad-spectrum antibiotic targeting Gram-positive bacteria, effective against skin infections and methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization.
• It functions by inhibiting protein synthesis via the isoleucyl-tRNA synthetase (IleRS) enzyme, crucial for amino acid incorporation.
• Bacteria possess two distinct IleRS types: IleRS1 (mupirocin-susceptible) and IleRS2 (mupirocin-resistant), originating from an early gene duplication event.

Purpose of the Study:

• To investigate the structural basis of mupirocin resistance conferred by IleRS2.
• To understand the mechanisms underlying high-level and hyper-resistance to mupirocin.
• To explore the evolutionary divergence of IleRS types and their clinical implications.

Main Methods:

• Comparative analysis of IleRS1 and IleRS2 structures and their interactions with mupirocin.
• Biochemical characterization of wild-type and variant IleRS enzymes, including kinetic assays (Ki values).
• Examination of the catalytic motif in hyper-resistant IleRS2 variants.

Main Results:

• IleRS2 resistance stems from altered interactions, notably the loss of hydrogen bonding to mupirocin's carboxylate moiety, compared to IleRS1.
• Recently identified hyper-resistant IleRS2 variants exhibit a non-canonical catalytic motif (swapped 1st and 3rd positions), crucial for resistance without compromising activity.
• Mupirocin resistance in clinical settings arises from IleRS1 mutations (low-level) or acquisition of plasmid-borne IleRS2 (high-level); hyper-resistant variants are not yet observed clinically.

Conclusions:

• The distinct evolutionary paths of IleRS1 and IleRS2 provide a basis for differential mupirocin susceptibility.
• The non-canonical catalytic motif in hyper-resistant IleRS2 represents a significant adaptation for evading antibiotic inhibition.
• Understanding these resistance mechanisms is vital for managing mupirocin efficacy and combating antibiotic resistance in bacterial pathogens.