Adenylating Enzymes in Mycobacterium tuberculosis as Drug Targets

Abstract

Adenylation or adenylate-forming enzymes (AEs) are widely found in nature and are responsible for the activation of carboxylic acids to intermediate acyladenylates, which are mixed anhydrides of AMP. In a second reaction, AEs catalyze the transfer of the acyl group of the acyladenylate onto a nucleophilic amino, alcohol, or thiol group of an acceptor molecule leading to amide, ester, and thioester products, respectively. Mycobacterium tuberculosis encodes for more than 60 adenylating enzymes, many of which represent potential drug targets due to their confirmed essentiality or requirement for virulence. Several strategies have been used to develop potent and selective AE inhibitors including high-throughput screening, fragment-based screening, and the rationale design of bisubstrate inhibitors that mimic the acyladenylate. In this review, a comprehensive analysis of the mycobacterial adenylating enzymes will be presented with a focus on the identification of small molecule inhibitors. Specifically, this review will cover the aminoacyl tRNA-synthetases (aaRSs), MenE required for menaquinone synthesis, the FadD family of enzymes including the fatty acyl-AMP ligases (FAAL) and the fatty acyl-CoA ligases (FACLs) involved in lipid metabolism, and the nonribosomal peptide synthetase adenylation enzyme MbtA that is necessary for mycobactin synthesis. Additionally, the enzymes NadE, GuaA, PanC, and MshC involved in the respective synthesis of NAD, guanine, pantothenate, and mycothiol will be discussed as well as BirA that is responsible for biotinylation of the acyl CoA-carboxylases.

Cyclic AMP-dependent Protein Lysine Acylation in Mycobacteria Regulates Fatty Acid and Propionate Metabolism

“…Strikingly, all tested substrates for KATmt (FadD22, FadD2, FadD5, and FadD13) belonged to the fatty acyl CoA synthetase family of proteins that activate lipids prior to their utilization in metabolic pathways (23). The site of acetylation of FadD22, FadD2, and FadD5 was the Lys residue present at a position equivalent to Lys-487 in FadD13.…”

Insight into Structure-Function Relationships and Inhibition of the Fatty Acyl-AMP Ligase (FadD32) Orthologs from Mycobacteria

“…By contrast, the degree of conservation of residues delineating the hydrophobic tunnel is lower, and changes in four residues that line the bottom of the tunnel (Leu-239 3 Phe-262, Phe-277 3 Tyr-301, Ala-279 3 Val-303, and Leu-310 3 Ile-333) might induce steric hindrance that could impede fully burying the aliphatic chains of the alkyl adenylate inhibitors. Several strategies have been developed for identifying and designing potent and selective mycobacterial AFE inhibitors (15). Bisubstrate inhibitors mimicking acyl adenylate, such as acylsulfamoyl adenosine and alkyl adenylate analogs (13, 41), appear to be good starting materials, but the rationale for their Gly-599, Arg-595, and Phe-625 residues, which are also strictly conserved in MtFadD32.…”

“…FACLs, FAALs, and other acyl-activating enzymes, such as the adenylation domains of non-ribosomal peptide synthetases, belong to the superfam-ily of adenylate-forming enzymes (AFEs) (14). The M. tuberculosis genome encodes more than 60 AFEs involved in numerous essential biochemical processes, which therefore constitute attractive targets for the development of new antituberculous drugs (15). FadD32 has been identified as an important susceptible (16) and potentially druggable (13,17,18) target.…”

Mechanism and Regulation of Mycobactin Fatty Acyl-AMP Ligase FadD33

“…ACS is an important enzyme for C2 carbon assimilation and metabolism. Moreover, ACS is also part of large family of acyl-activating enzyme, which includes FadDs enzymes along with non-ribosomal peptide synthetases (14).…”