Structure of a Hydroxymycolic Acid Potentially Involved in the Synthesis of Oxygenated Mycolic Acids of the Mycobacterium Tuberculosis Complex

Abstract

Mycolic acids are believed to play a crucial role in the architecture of the mycobacterial envelope. However, very few steps of their biosynthetic pathway have yet been elucidated. We previously isolated [Dubnau, E., Lanéelle, M. A., Soares, S., Bénichou, A., Vaz, T., Promé, D., Promé, J. C., Daffé, M. & Quémard, A. (1997) Mycobacterium bovis BCG genes involved in the biosynthesis of cyclopropyl keto and hydroxy‐mycolic acids, Mol. Microbiol. 23, 313–322] a gene cluster from Mycobacterium bovis BCG, cmaA‐D, which confers upon M. smegmatis the ability to synthesize cyclopropanated ketomycolic acid, and a new type of mycolic acid which is hydroxylated. A meticulous analysis of all the mycolic like fatty acids of M. bovis BCG and M. tuberculosis showed that these organisms produce small amounts of the hydroxymycolic acid. The structure of this molecule, determined by NMR spectroscopy, mass spectrometry and stereochemical studies, strongly suggests that there is a direct biosynthetic relationship between the keto‐and the hydroxyl‐mycolic acids.

Towards understanding the functional diversity of cell wall mycolic acids of Mycobacterium tuberculosis

“…There is a perfect match between the structures of the keto-and hydroxy-MA [62]. More detailed analysis showed that both M.bovis BCG and M.tuberculosis also produce small amounts of hydroxy-MA and again there appears to be a direct relationship between hydroxy-MA and keto-MA [63]. Although cyclopropanated MAs were previously thought not to abound in M.smegmatis, it was recently shown that the genes to effect this are present in the genome and can be induced for expression at low temperature growth conditions [65].…”

Trafficking pathways of mycolic acids: structures, origin, mechanism of formation, and storage form of mycobacteric acids

“…They have been isolated from a large variety of mycobacteria [e.g., M. tuberculosis (11,12), M. smegmatis (15), M. kansasii (41), and from a species of Nocardia (17)]. In the present work, a series of C [35][36][37][38][39] acids with odd and even numbers of carbon atoms and containing trans and cis double bonds was characterized and shown to be structurally related to the mycolic acids of M. brumae (28). Two pools of fatty acids, with C 39 and C 51 as the main terms, were also characterized in M. fallax and were shown to contain double bonds located at the same positions as in the meromycolic chain of the mycolic acids of this species.…”

“…The accelerating voltage was 8 kV, the electron energy was 70 eV, the source temperature was set at 250°C. The temperature of the solid probe was ramped from 100°C to 300°C in 10 min (35). The same instrument (provided with a caesium gun, 25 kV) was employed for fast-atom bombardment-MS in positive and negative modes; the accelerating voltage was 8 kV and the matrix used was m-nitrobenzyl alcohol.…”

“…For instance, keto and methoxyl groups were shown to occur in mycobacteric acids and mycolic acids isolated from M. tuberculosis (11); similarly, keto and wax functions were found in both types of fatty acids isolated from M. aurum (16). A series of shorter homologous fatty acids have been also isolated from triacylglycerols (TAGs) of a Nocardia species; these consist in C [35][36][37][38][39][40][41][42][43][44][45] fatty acids containing 3 and 4 double bonds as observed in nocardomycolic acids (17). In addition, long-chain ketones and secondary alcohols parented to mycolic acids have been also found in mycobacteria (e.g., the so-called C 80 mycolones and mycolols) (18,19), in nocardia (C 50-60 nocardones, nocardols) (20)(21)(22)(23), and in corynebacteria (16-hentriacontanone or palmitone) (24,25).…”

“…Mycobacteria contain structurally related long-chain lipids, but the metabolic relationships between these various classes of compounds remain obscure. To address this question a series of C 35 to C 54 nonhydroxylated fatty acids (mycobacteric acids), ketones, and alcohols structurally related to the C 70-80 dicyclopropanated or diethylenic mycolic acids were characterized in three mycobacterial strains and their structures compared. The relationships between these longchain acids and mycolic acids were established by following the in vivo traffic of 14 C labeled a-mycolic acids purified from the same mycobacterial species.…”