Aminoglycoside 2′-N-acetyltransferase from Mycobacterium tuberculosis in complex with coenzyme A and aminoglycoside substrates

AAC(2')-Ic catalyzes the coenzyme A (CoA)-dependent acetylation of the 2 hydroxyl or amino group of a broad spectrum of aminoglycosides. The crystal structure of the AAC(2')-Ic from Mycobacterium tuberculosis has been determined in the apo enzyme form and in ternary complexes with CoA and either tobramycin, kanamycin A or ribostamycin, representing the first structures of an aminoglycoside acetyltransferase bound to a drug. The overall fold of AAC(2')-Ic places it in the GCN5-related N-acetyltransferase (GNAT) superfamily. Although the physiological function of AAC(2')-Ic is uncertain, a structural analysis of these high-affinity aminoglycoside complexes suggests that the enzyme may acetylate a key biosynthetic intermediate of mycothiol, the major reducing agent in mycobacteria, and participate in the regulation of cellular redox potential.