The effect of oxygenated mycolic acid composition on cell wall function and macrophage growth in Mycobacterium tuberculosis

Abstract

There are three major structural classes of mycolic acids in the cell envelope of Mycobacterium tuberculosis (MTB): alpha-, methoxy- and ketomycolate. The two oxygen-containing classes are biosynthetically related through a common alpha-methyl hydroxymycolate intermediate. BCG strains that fail to produce methoxymycolate and instead produce only keto- and alpha-mycolic acids show apparent defects in the O-methyltransferase MMAS-3. Overproduction of MMAS-3 from MTB resulted in a complete replacement of ketomycolate by methoxymycolate in both BCG and MTB. In vitro growth of these recombinant strains lacking ketomycolate was impaired at reduced temperatures but appeared to be normal at 37 degrees C. Glucose uptake was significantly decreased in such strains, but uptake of chenodeoxycholate and glycine was unaffected. Although sensitivity to INH remained unchanged, these cells were found to be hypersensitive to ampicillin and rifampicin. Infectivity of BCG and H37Rv wild type or MMAS-3 overproducers in THP-1 cells was somewhat affected, but the ability of the strains lacking ketomycolate to grow within this macrophage-like cell line was severely compromised. In vivo labelling of mycolic acids during growth of H37Rv within THP-1 cells revealed a substantial increase in ketomycolate and alphamycolate synthesized by intracellularly grown mycobacteria. These results establish a critical role for mycolate composition in proper cell wall function during the growth of MTB in vivo.

The mmaA2 Gene of Mycobacterium tuberculosis Encodes the Distal Cyclopropane Synthase of the α-Mycolic Acid

“…To confirm this structure in more detail, we performed two-dimensional 1 H COSY NMR of the mmaA2 mutant ␣-mycolate. This study revealed that the vinyl protons are adjacent to protons at 2.02 ppm, consistent with previously reported resonances of vinyl protons in meromycolate chains (data not shown) (23). These findings are similar to our previous NMR findings when examining the ␣-mycolate of the pcaA mutant and establish that the mmaA2 mutant ␣-mycolate lacks either a proximal or distal cyclopropyl group.…”

Bacterial immunostat: Mycobacterium tuberculosis lipids and their role in the host immune response

“…MA cyclopropane ring is required for virulence and long-term persistence of pathogenic mycobacteria in mice 33,34 . Also, the relative differences in the amounts of keto-and methoxy-MA influence the intra-macrophage growth rate of M. tuberculosis 35 and the absence of keto-and methoxy-MA is associated with bacterial attenuation in mice 36 . The abundance of MA in M. tuberculosis cell wall appears to affect the course of tuberculosis in infected people.…”

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

“…Whereas this diminishes the prospects of increasing the accuracy of mycolic acid antigen based immunodiagnostic tests for TB by using particular isomers of chemically synthetic mycolic acids, it eases the necessity for defining exactly the class composition of MA antigens that is used to detect the MA-binding antibodies. These MAs may resemble early stage M. tuberculosis when the keto-MA dominates or the late stage when the methoxy-MA dominates [131], with the only difference being slight changes in the magnitude of the signals for both MA antigen sets, with no difference in the ratio of the antibody binding signal from TB positive and TB negative patients.…”