UC San Diego

Lipoic acid is an essential cofactor produced in all organisms by diverting octanoic acid derived as an intermediate of type II fatty acid biosynthesis. In bacteria, octanoic acid is transferred from the acyl carrier protein (ACP) to the lipoylated target protein by the octanoyltransferase LipB. LipB has a well-documented substrate selectivity, indicating a mechanism of octanoic acid recognition. The present study reveals the precise protein-protein interactions (PPIs) responsible for this selectivity in Escherichia coli through a combination of solution-state protein NMR titration with high-resolution docking of the experimentally examined substrates. We examine the structural changes of substrate-bound ACP and determine the precise geometry of the LipB interface. Thermodynamic effects from varying substrates were observed by NMR, and steric occlusion of docked models indicates how LipB interprets proper substrate identity via allosteric binding. This study provides a model for elucidating how substrate identity is transferred through the ACP structure to regulate activity in octanoyl transferases.