Structural Basis for Targeting the Bifunctional Enzyme ArnA.

Area of Science:

• Microbiology
• Structural Biology
• Drug Discovery

Background:

• Polymyxin antibiotics are critical for treating multidrug-resistant Gram-negative infections.
• Resistance often involves modifying lipid A with 4-amino-4-deoxy-L-arabinose (L-Ara4N) via the ArnA enzyme.
• The evolutionary and structural mechanisms of ArnA's function are not fully understood.

Purpose of the Study:

• To elucidate the evolutionary origins and structural basis of ArnA's bifunctional enzyme activity.
• To understand the molecular mechanisms behind ArnA's hexameric assembly and catalytic coordination.
• To identify potential therapeutic targets for inhibiting L-Ara4N biosynthesis.

Main Methods:

• Evolutionary genomics to trace domain evolution.
• High-resolution cryo-electron microscopy (cryo-EM) to determine ArnA structure.
• Computational protein design to develop inhibitors.

Main Results:

• The dehydrogenase (DH) and formyltransferase (TF) domains of ArnA fused selectively in Gammaproteobacteria.
• A cryo-EM structure revealed a DH-driven hexameric architecture crucial for ArnA activity.
• Computational design yielded peptide inhibitors targeting ArnA hexamerization.

Conclusions:

• ArnA's domain fusion provided an adaptive advantage in antimicrobial resistance.
• ArnA's hexameric structure is key to its enzymatic function and a potential drug target.
• Inhibiting L-Ara4N biosynthesis through ArnA offers a novel therapeutic strategy against resistant pathogens.