Structural Insightsinto Lipoate Ligase A‑MediatedAntibody Modifications

Enzyme-mediated site-specific protein modification is gaining attention in biopharmaceuticals due to its high specificity and mild conditions. Lipoic acid ligase A (LplA) has been widely studied for conjugating short-chain fatty acids to lysine residues, traditionally using LAP tags. Recent advances have enabled tag-free LplA modifications, expanding applications in antibody-drug conjugates (ADCs) and beyond. This study investigates the selective modification of Lys188 in trastuzumab by LplA. Spatial analysis and molecular modeling suggest that D151 and H189 facilitate nucleophilic attack and stabilize intermediates via electrostatic and π-cation interactions. These insights enhance our understanding of enzyme-driven site selectivity, guiding the rational design of antibody modifications. The findings support broader applications in ADC production, diagnostics, and next-generation biopharmaceuticals, emphasizing the role of local amino acid environments in enzymatic modifications.