Isocitrate lyase is important for lipid utilisation by Mycobacterium tuberculosis but its ICL2 isoform is poorly understood. Here we report that binding of the lipid metabolites acetyl-CoA or propionyl-CoA to ICL2 induces a striking structural rearrangement, substantially increasing isocitrate lyase and methylisocitrate lyase activities. Thus, ICL2 plays a pivotal role regulating carbon flux between the tricarboxylic acid (TCA) cycle, glyoxylate shunt and methylcitrate cycle at high lipid concentrations, a mechanism essential for bacterial growth and virulence.

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Mycobacterium tuberculosis isocitrate lyases (ICLs) form a covalent adduct with itaconate through their catalytic cysteine residue. These results reveal atomic details of itaconate inhibition and provide insights into the catalytic mechanism of ICLs.

The enzymes isocitrate lyase (ICL) isoforms 1 and 2 are essential for Mycobacterium tuberculosis survival within macrophages during latent tuberculosis (TB). Herein we report the development of a combined NMR spectroscopy and thermal shift assay for the screening and evaluation of ICL inhibitors.

Isocitrate lyase (ICL) isoform 2 is an essential enzyme for some clinical Mycobacterium tuberculosis (Mtb) strains during infection. In the laboratory Mtb strain H37Rv, the icl2 gene encodes two distinct gene products – Rv1915 and Rv1916 – due to a frameshift mutation. This study aims to characterise these two gene products to understand their structure and function. While we were unable to produce Rv1915 recombinantly, soluble Rv1916 was obtained with sufficient yield for characterisation. Kinetic studies using UV‐visible spectrophotometry and 1H‐NMR spectroscopy showed that recombinant Rv1916 does not possess isocitrate lyase activity, while waterLOGSY binding experiments demonstrated that it could bind acetyl‐CoA. Finally, X‐ray crystallography revealed structural similarities between Rv1916 and the C‐terminal domain of ICL2. Considering the probable differences between full‐length ICL2 and the gene products Rv1915 and Rv1916, care must be taken when using Mtb H37Rv as a model organism to study central carbon metabolism.