Functional and mechanistic insights into the stealth protein full-length CpsY is conducive to understanding immune evasion mechanisms by Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) is a crucial and destructive intracellular pathogen responsible for causing tuberculosis (TB), a disease of substantial morbidity and mortality. Mtb capsular polysaccharides can misdirect the host's immune response pathways, resulting in additional challenges in TB treatment. These capsule polysaccharides are biosynthesized by a series of stealth proteins including CpsY. Our prior investigations elucidated the structural and functional information of the central domain (aa 201–520) of CpsY within Mtb. However, within the host milieu, it is the full-length iteration of CpsY, rather than its truncated form CpsY^201-520, that assumes pivotal roles in immune evasion. Consequently, investigating the functional mechanism of full-length CpsY is extremely important. Here, we found that the indispensable role of four conserved regions (CR1-CR4) in governing the phosphotransferase activity of full-length CpsY. Notably, the deletion of S2 (ΔS2) dramatically increased the activity compared to the wild-type (WT) full-length CpsY, thereby revealing S2 in the regulatory dynamics governing the inactivation and activation of full-length CpsY. The gene cpsY helps Mtb to survive in macrophages. Our findings were useful for the development of vaccines and immunotherapies targeting Mtb.