The changes in mycolic acid structures caused by hadC mutation have a dramatic effect on the virulence of Mycobacterium tuberculosis

Abstract

SummaryUnderstanding the molecular strategies used by Mycobacterium tuberculosis to invade and persist within the host is of paramount importance to tackle the tuberculosis pandemic. Comparative genomic surveys have revealed that hadC, encoding a subunit of the HadBC dehydratase, is mutated in the avirulent M. tuberculosis H37Ra strain. We show here that mutation or deletion of hadC affects the biosynthesis of oxygenated mycolic acids, substantially reducing their production level. Additionally, it causes the loss of atypical extra-long mycolic acids, demonstrating the involvement of HadBC in the late elongation steps of mycolic acid biosynthesis. These events have an impact on the morphotype, cording capacity and biofilm growth of the bacilli as well as on their sensitivity to agents such as rifampicin. Furthermore, deletion of hadC leads to a dramatic loss of virulence: an almost 4-log drop of the bacterial load in the lungs and spleens of infected immunodeficient mice. Both its unique function and importance for M. tuberculosis virulence make HadBC an attractive therapeutic target for tuberculosis drug development.

Deletion of a dehydratase important for intracellular growth and cording renders rough Mycobacterium abscessus avirulent

“…Among them, trehalose-dimycolate (TDM; also known as cord factor) is implicated in various biological functions, such as pathogenesis, immunomodulation, inflammation, granuloma formation, or cording (43,44). Strikingly, the cord-deficient phenotype of ΔMAB_4780 that may directly result from the changes in the mycolic acid pattern provides an ideal tool to unravel the role of cording in pathogenesis of Mabs R. Indeed, disruption of MAB_4780 abrogated all pathophysiological traits of the R strain-virulence, neurotropism, intramacrophage survival, granuloma formation, and cording-emphasizing the critical role of MAB_4780 in pathogenicity of Mabs R. It is worth mentioning that mutation/deletion of hadC also impacts cording and virulence of M. tuberculosis in mice (22), further underlining the redundant functions between MAB_4780 and HadBC. Interestingly, whereas MAB_4780 is needed for cording in Mabs, a functional ortholog (MSMEG_6754) is present in the noncording M. smegmatis and no orthologs are apparently present in M. tuberculosis, a known cording species.…”

“…A possible explanation could be that HadBC activity may be deficient in these species due to a defect in gene expression or regulation. A mutation or deletion of hadC affects the biosynthesis of oxygenated mycolic acids in M. tuberculosis, substantially reducing their production and demonstrating the involvement of HadBC in the late elongation steps (22). Combined with our findings that, like HadBC, MAB_4780 exhibits a substrate preference for long fatty acyl chains (C 12 but not C 4 ) and that a change in the α/α′-mycolic acid ratio occurs in ΔMAB_4780, it can be inferred that MAB_4780 participates also in the last elongation steps of meromycolic acid biosynthesis.…”

“…Moreover, deletion of hadC in M. tuberculosis correlates with a loss of cording and attenuation of virulence in infected mice (22), thus emphasizing the intimate interplay between TAC resistance, mycolic acid biosynthesis, cording, and virulence. We have previously shown that Mycobacterium smegmatis possesses a gene, MSMEG_6754, responsible for its remarkable resistance to TAC and involved in mycolic acid metabolism and that disruption of MSMEG_6754 in M. smegmatis was associated with impaired growth in Acanthamoeba castellanii (23).…”

Mycolates of Mycobacterium tuberculosis modulate the flow of cholesterol for bacillary proliferation in murine macrophages

“…HadC is a dehydratase that is not catalytically active, but holds the longer form of the elongating merochain of MA in a complex with HadB, which catalyzes dehydration of a -hydroxyacyl in the merochain to an enoyl. The hadC KO Mtb H37Rv showed a reduction in the abundance of mMA similar to that found in Mtb H37Ra (62). Accordingly, it also had lower virulence, approximating that of Mtb H37Ra, lost its cording and biofilming ability, and its envelope integrity, thus making it more susceptible to the hydrophobic drug, rifampicin.…”

Structure-aware M. tuberculosis functional annotation uncloaks resistance, metabolic, and virulence genes

“…Mycolic acids feature prominently in the repertoire of pathogenic weaponry wielded by M. tuberculosis and are essential to virulence 47 .…”