ArnA_N: ArnA is a bifunctional enzyme required for the modification of lipid A with 4-amino-4-deoxy-L-arabinose (Ara4N) that leads to resistance to cationic antimicrobial peptides (CAMPs) and clinical antimicrobials such as polymyxin. The C-terminal dehydrogenase domain of ArnA catalyzes the oxidative decarboxylation of UDP-glucuronic acid (UDP-GlcUA) to UDP-4-keto-arabinose (UDP-Ara4O), while the N-terminal formyltransferase domain of ArnA catalyzes the addition of a formyl group to UDP-4-amino-4-deoxy-L-arabinose (UDP-L-Ara4N) to form UDP-L-4-formamido-arabinose (UDP-L-Ara4FN). This domain family represents the catalytic core of the N-terminal formyltransferase domain. The formyltransferase also contains a smaller C-terminal domain the may be involved in substrate binding. ArnA forms a hexameric structure, in which the dehydrogenase domains are arranged at the center of the particle with the transformylase domains on the outside of the particle.
Comment:Mutation experiments identified key catalytic residues Asn(102), His(104), and Asp(140) from Escherichia coli ArnA protein for the formyl transferase activity.
Jiyao W et al.(2023). "The conserved domain database in 2023.",