ACCase 6 is the essential acetyl-CoA carboxylase involved in fatty acid and mycolic acid biosynthesis in mycobacteria

Abstract

Mycolic acids are essential for the survival, virulence and antibiotic resistance of the human pathogen Mycobacterium tuberculosis. Inhibitors of mycolic acid biosynthesis, such as isoniazid and ethionamide, have been used as efficient drugs for the treatment of tuberculosis. However, the increase in cases of multidrug-resistant tuberculosis has prompted a search for new targets and agents that could also affect synthesis of mycolic acids. In mycobacteria, the acyl-CoA carboxylases (ACCases) provide the building blocks for de novo fatty acid biosynthesis by fatty acid synthase (FAS) I and for the elongation of FAS I products by the FAS II complex to produce meromycolic acids. By generating a conditional mutant in the accD6 gene of Mycobacterium smegmatis, we demonstrated that AccD6 is the essential carboxyltransferase component of the ACCase 6 enzyme complex implicated in the biosynthesis of malonyl-CoA, the substrate of the two FAS enzymes of Mycobacterium species. Based on the conserved structure of the AccD5 and AccD6 active sites we screened several inhibitors of AccD5 as potential inhibitors of AccD6 and found that the ligand NCI-172033 was capable of inhibiting AccD6 with an IC 50 of 8 mM. The compound showed bactericidal activity against several pathogenic Mycobacterium species by producing a strong inhibition of both fatty acid and mycolic acid biosynthesis at minimal inhibitory concentrations. Overexpression of accD6 in M. smegmatis conferred resistance to NCI-172033, confirming AccD6 as the main target of the inhibitor. These results define the biological role of a key ACCase in the biosynthesis of membrane and cell envelope fatty acids, and provide a new target, AccD6, for rational development of novel anti-mycobacterial drugs.

AccD6, a Key Carboxyltransferase Essential for Mycolic Acid Synthesis in Mycobacterium tuberculosis, Is Dispensable in a Nonpathogenic Strain

“…Using this technique, we provided compelling evidence that accD6 is indeed an essential gene in M. tuberculosis under the culture conditions described, thereby confirming the previous predictive data. However, in contrast to the previous report by Kurth et al (36), we were able to remove the functional accD6 gene from the chromosome of M. smegmatis. Deletion of accD6 in M. smegmatis was performed in two independent experiments and was confirmed by all typical techniques, as described in Results.…”

“…However, due to the essential nature of accD6, the possible involvement of AccD6 in mycolic acid biosynthesis has never been addressed in vivo. Until now, only one study concerning the probable function of accD6 in the fast-growing nonpathogenic species Mycobacterium smegmatis has been conducted (36).…”

Early diagnosis and effective treatment regimens are the keys to tackle antimicrobial resistance in tuberculosis (TB): A report from Euroscicon's international TB Summit 2016

“…Mammalian cells acquire biotin from the external environment and thus lack these enzymes, therefore validating this pathway for developing intrinsically selective anti-TB drugs. 117 Furthermore, mutants in the biotin synthesis pathway can cause only attenuated forms of infections in mice, suggesting the pathogen is unable to obtain exogenous biotin. 118 Prof Schnappinger and his group found that mutating one of the enzymes, BioA (biotin ligase) in M. tuberculosis made it incapable of surviving in vitro and in mice indicating that the de novo biotin synthesis is critical for the pathogen's survival and persistence.…”

Brief Approach of Herbicide Resistance in Context of Crops Development Worldwide

“…It catalyzes the ATP dependent carboxylation of Acetyl CoA to form malonyl CoA, which is the precursor of fatty acids (Sellwood et al, 2000). It is present in prokaryotes, chloroplasts of most plants and algae, endoplasmic reticulum of most eukariotes, and even mycobacteria (Kurth et al, 2009). ACCase catalyses two partial reaction occurring at two different sites (Fig.…”