Visualizing the Adenylation Activities and Protein-Protein Interactions of Aryl Acid Adenylating Enzymes.

Structural and activity studies have revealed the dynamic and transient actions of carrier protein (CP) activity in primary and secondary metabolic pathways. CP-mediated interactions play a central role in nonribosomal peptide biosynthesis, as they serve as covalent tethers for amino acid and aryl acid substrates and enable the growth of peptide intermediates. Strategies are therefore required to study protein-protein interactions efficiently. Herein, we describe activity-based probes used to demonstrate the protein-protein interactions between aryl CP (ArCP) and aryl acid adenylation (A) domains as well as the substrate specificities of the aryl acid A domains. If coupled with in-gel fluorescence imaging, this strategy allows visualization of the protein-protein interactions required to recognize and transfer the substrate to the partner ArCP. This technique has potential for the analysis of protein-protein interactions within these biosynthetic enzymes at the molecular level and for use in the combinatorial biosynthesis of new nonribosomal peptides.