GlnR-mediated regulation of KstR controls cholesterol catabolism in Mycobacterium smegmatis

Tuberculosis, caused by mycobacteria, continues to pose a substantial public health threat. Mycobacteria typically use cholesterol from the membranes of host macrophages as a carbon and energy source. Most genes that control cholesterol degradation are regulated by KstR, which is highly conserved in Mycobacterium tuberculosis and Mycobacterium smegmatis. Through bioinformatic analysis, we found a typical global nitrogen regulator (GlnR)-binding motif (CCGAC-AACAGT-GACAC) in the promoter region of kstR of M. smegmatis, and we determined its binding activity in vitro using electrophoretic mobility shift assays. Using RT-qPCR, we found that nine genes involved in side-chain or sterol-ring oxidation were upregulated in a ΔglnR M. smegmatis strain compared to the WT strain and glnR-complemented strains under nitrogen limitation. ATP assays in macrophages revealed that coordinated GlnR-KstR regulation significantly reduced the viability of M. smegmatis in macrophages. Thus, we found that various genes involved in cholesterol catabolism are regulated by GlnR via KstR in response to environmental nitrogen, and that they further affect the invasive ability of M. smegmatis. These findings revealed a novel regulatory mechanism of cholesterol catabolism, which may be useful in the development of new strategies for controlling tuberculosis.