Role of long-chain acyl-CoAs in the regulation of mycolic acid biosynthesis in mycobacteria

Abstract

One of the dominant features of the biology of Mycobacterium tuberculosis, and other mycobacteria, is the mycobacterial cell envelope with its exceptional complex composition. Mycolic acids are major and very specific components of the cell envelope and play a key role in its architecture and impermeability. Biosynthesis of mycolic acid (MA) precursors requires two types of fatty acid synthases, FAS I and FAS II, which should work in concert in order to keep lipid homeostasis tightly regulated. Both FAS systems are regulated at their transcriptional level by specific regulatory proteins. FasR regulates components of the FAS I system, whereas MabR and FadR regulate components of the FAS II system. In this article, by constructing a tight mabR conditional mutant in Mycobacterium smegmatis mc2155, we demonstrated that sub-physiological levels of MabR lead to a downregulation of the fasII genes, inferring that this protein is a transcriptional activator of the FAS II system. In vivo labelling experiments and lipidomic studies carried out in the wild-type and the mabR conditional mutant demonstrated that under conditions of reduced levels of MabR, there is a clear inhibition of biosynthesis of MAs, with a concomitant change in their relative composition, and of other MA-containing molecules. These studies also demonstrated a change in the phospholipid composition of the membrane of the mutant strain, with a significant increase of phosphatidylinositol. Gel shift assays carried out with MabR and PfasII as a probe in the presence of different chain-length acyl-CoAs strongly suggest that molecules longer than C18 can be sensed by MabR to modulate its affinity for the operator sequences that it recognizes, and in that way switch on or off the MabR-dependent promoter. Finally, we demonstrated the direct role of MabR in the upregulation of the fasII operon genes after isoniazid treatment.

Path‐seq identifies an essential mycolate remodeling program for mycobacterial host adaptation

“…The question remains how MadR is able to differentially bind to DNA in response to environmental changes. In mycobacteria, other TFs regulating mycolate biosynthesis are modulated by long‐chain acyl‐CoAs (Biswas et al , ; Mondino et al , ; Tsai et al , ), proposing a role for these molecules in the modulation of MadR as well. Similarly, a MadR homolog in Pseudomonas aeruginosa , DesT, was shown to have enhanced DNA binding in the presence of unsaturated acyl‐CoAs (Zhang et al , ).…”

Lipid metabolism and its implication in mycobacteria–host interaction

“…The first transcriptional regulator of the main fasII operon ( fabD-acpM-kasA-kasB ) that was characterized is MabR [48]. Genetic studies showed that mabR is essential for M. smegmatis survival and biochemical analysis carried out in a mabR conditional mutant strain showed alterations in mycolic acid and in de novo FA biosynthesis, demonstrating for the first time the existence of a crosstalk between the two FAS systems and confirming MabR as one of the key modulator of lipid homeostasis in Mycobacterium [48,49]. A second non-essential transcription factor, FadR, that represses the fasII operon expression has also been described [50].…”

“…Analysis of a conditional mutant in M. smegmatis showed that FasR is a transcriptional activator and proved its essential role in mycobacteria viability. Interestingly, the activity of all these transcription factors (MabR, FadR and FasR) is modulated by long chain acyl-CoAs, the products of the FAS I system, highlighting a key role for these molecules in the modulation of lipid biosynthesis in mycobacteria [49,50,53]. An important difference between MabR and FasR with other bacteria transcriptional regulators of FA biosynthesis is that these two proteins are essential for bacterial survival while all the others are not.…”

Extracytoplasmic function sigma factor σD confers resistance to environmental stress by enhancing mycolate synthesis and modifying peptidoglycan structures in Corynebacterium glutamicum

“…MA synthesis is regulated at the fatty acid synthesis step. Fatty acid synthase genes are transcriptionally regulated in response to acyl‐CoA in C. glutamicum and mycobacteria (Nickel et al ., ; Salzman et al ., ; Mondino et al ., ; Irzik et al ., ; Tsai et al ., ). Moreover, FAS‐II components in M. tuberculosis are post‐translationally regulated by Ser/Thr protein kinase‐mediated phosphorylation (Molle et al ., ; Bhatt et al ., ; Slama et al ., ; Vilcheze et al ., ).…”