7,8‐Diaminoperlargonic acid aminotransferase from Mycobacterium tuberculosis, a potential therapeutic target

Abstract

Diaminopelargonic acid aminotransferase (DAPA AT), which is involved in biotin biosynthesis, catalyzes the transamination of 8-amino-7-oxononanoic acid (KAPA) using S-adenosyl-l-methionine (AdoMet) as amino donor. Mycobacterium tuberculosis DAPA AT, a potential therapeutic target, has been overproduced in Escherichia coli and purified to homogeneity using a single efficient step on a nickel-affinity column. The enzyme shows an electronic absorption spectrum typical of pyridoxal 5'-phosphate-dependent enzymes and behaves as a homotetramer in solution. The pH profile of the activity at saturation shows a single ionization group with a pK(a) of 8.0, which was attributed to the active-site lysine residue. The enzyme shows a Ping Pong Bi Bi kinetic mechanism with strong substrate inhibition with the following parameters: K(mAdoMet) = 0.78 +/- 0.20 mm, K(mKAPA) = 3.8 +/- 1.0 microm, k(cat) = 1.0 +/- 0.2 min(-1), K(iKAPA) = 14 +/- 2 microm. Amiclenomycin and a new analogue, 4-(4c-aminocyclohexa-2,5-dien-1r-yl)propanol (referred to as compound 1), were shown to be suicide substrates of this enzyme, with the following inactivation parameters: K(i) = 12 +/- 2 microm, k(inact) = 0.35 +/- 0.05 min(-1), and K(i) = 20 +/- 2 microm, k(inact) = 0.56 +/- 0.05 min(-1), for amiclenomycin and compound 1, respectively. The inactivation was irreversible, and the partition ratios were 1.0 and 1.1 for amiclenomycin and compound 1, respectively, which make these inactivators particularly efficient. compound 1 (100 microg.mL(-1)) completely inhibited the growth of an E. coli C268bioA mutant strain transformed with a plasmid expressing the M. tuberculosis bioA gene, coding for DAPA AT. Reversal of the antibiotic effect was observed on the addition of biotin or DAPA. Thus, compound 1 specifically targets DAPA AT in vivo.