Enzyme-mediated aminoglycoside resistance without target mimicry

Area of Science:

• Molecular Biology
• Structural Biology
• Antimicrobial Resistance

Background:

• Aminoglycoside antibiotics are crucial for treating bacterial infections.
• Resistance to these antibiotics commonly arises from enzymatic modification.
• Existing research suggests these modifying enzymes mimic the antibiotic's target, the bacterial ribosome A site.

Purpose of the Study:

• To investigate aminoglycoside-modifying enzymes that deviate from the typical target mimicry mechanism.
• To elucidate the structural and functional characteristics of AAC(3)-Ia and AAC(3)-XIa.
• To determine if target mimicry is essential for aminoglycoside resistance conferred by these enzymes.

Main Methods:

• X-ray diffraction studies to determine enzyme-antibiotic binding structures.
• In silico and in vitro assays to assess antibiotic modification efficiency.
• In vivo studies to evaluate the enzymes' role in conferring resistance.

Main Results:

• Two novel enzymes, AAC(3)-Ia and AAC(3)-XIa, were identified that do not employ target mimicry.
• Structural analysis revealed these enzymes bind aminoglycosides in a non-canonical 'boat' conformation.
• Functional and in vivo assessments confirmed these enzymes effectively confer resistance despite lacking target mimicry.

Conclusions:

• Target mimicry is not an absolute requirement for aminoglycoside-modifying enzymes to confer resistance.
• Alternative binding modes, such as the observed boat conformation, can be effective.
• This finding broadens our understanding of antibiotic resistance mechanisms and potential therapeutic strategies.