Elucidating the role of mannosylated cell surface glycoconjugates for pathogenesis of Mycobacterium tuberculosis (Manno-TB)

• Applicant: Professor Dr. Rainer Kalscheuer
• Subject Area: Medical Microbiology and Mycology, Hygiene, Molecular Infection Biology ; Parasitology and Biology of Tropical Infectious Disease Pathogens
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 501771662

The success of Mycobacterium tuberculosis (Mtb) as one of the most serious human pathogens is largely attributable to its peculiar cell wall structure. In addition to the characteristic mycolic acids, mycobacteria possess various additional unique cell wall molecules that confer exceptional physicochemical resistance to various stresses and/or play important roles in interaction with the host´s immune system. Some of the most abundant cell wall molecules are rich in mannose: phosphatidylinositol mannosides, lipomannan, lipoarabinomannan, arabinomannan, and mannosylated glycoproteins. Several of these mannosylated glycoconjugates (Man-GlyCs) are important for Mtb viability, and enzymes involved in their synthesis represent potential drug targets. As surface-exposed molecules, the highly immunogenic Man-GlyCs also play a central role in host-pathogen interaction, and many of them interact with different host cell receptors. In vitro studies using purified molecules indicate that anti-inflammatory immune responses dominate and suggest that Mtb might exploit Man-GlyCs for immunosuppressive C-type lectin receptor signalling as a strategy to escape immune surveillance. Mycobacterial mutants lacking individual Man-GlyC species or exhibiting only slightly reduced Man-GlyC levels, however, did not show profoundly altered virulence and pathogenic traits. Due to high functional redundancy and promiscuity in the Man-GlyC/receptor interactions, we hypothesize that the interaction of Mtb with the host might not be dominated by specific Man-GlyCs but rather by the total degree of cell surface mannosylation. Essentiality of some ManGlyCs, however, have prevented the generation of Mtb mutants with substantially reduced levels of total cell surface mannosylation. Thus, the role of Man-GlyCs for pathogenicity of Mtb on the whole-cell level is still largely elusive. In this German-South-African cooperation project, we propose to use conditional gene silencing targeting essential enzymes that are involved in early steps of Man-GlyC biosynthesis in order to generate Mtb mutants that exhibit a substantial reduction in total cell surface mannosylation. Partially gene silencing in the conditional Mtb mutants will allow growth but at the same time already substantially depletes Man-GlyCs. This will allow dissection of the immunomodulatory properties of Man-GlyCs largely independent of their function in maintaining viability of Mtb.using cellular, an organoid 3D human spheroid and TB animal models. These studies will deepen our understanding of how Mtb might use specific Man-GlyCs to control immunomodulation during different phases of infection. In the long-term, findings from this project might inform drug development efforts as well as the development of new diagnostic tools that rely on antigenic recognition of specific Man-GlyCs and might enable the rational design of more immunogenic Mycobacterium bovis BCG live TB vaccines.

• DFG Programme: Research Grants
• International Connection: South Africa
• International Co-Applicant: Professor Adrie JC Steyn, Ph.D.