Cell envelope integrity in mycobacteria: interplay of lipoglycans, peptidoglycan, and capsular polysaccharides

项目总结

PROJECT SUMMARY Lipomannan (LM) and lipoarabinomannan (LAM) are mycobacterial lipoglycans that are critical for Mycobacte- rium tuberculosis to establish infection. These lipoglycans are synthesized in the plasma membrane and trafficked to the cell surface. LM and LAM are widely conserved among mycobacteria, and therefore must also play a fundamental role in the physiology of both pathogenic and nonpathogenic mycobacterial species. However, it remains obscure how their biosynthesis is coordinated with other cell envelope biosyntheses and how they contribute to the integrity of the cell envelope. The long-term goal is to determine the role of lipoglycans in my- cobacterial physiology and identify vulnerabilities in the process of creating and maintaining the cell envelope structure. As the next step, the objective of this proposal is to gain fundamental insights into the role of lipogly- cans in cell envelope integrity in Mycobacterium smegmatis and M. tuberculosis. The central hypothesis is that LM/LAM biosynthesis, in coordination with peptidoglycan and capsular a-glucan biosyntheses, positively con- tributes to glycan homeostasis, ensuring the plasticity and integrity of cell surface structure during active growth. The rationale is that finding vulnerabilities in the regulatory process that coordinates the glycan biosyntheses will lay the foundation for cell envelope-targeting antimicrobial development. Guided by published and preliminary data from the applicant’s laboratory, this hypothesis will be tested by pursuing two aims: 1) Identify the role of LM/LAM biosynthesis in suppressing peptidoglycan degradation; and 2) Determine the role of the capsular layer in maintaining cell envelope integrity. In the first aim, the hypothesis that the cell shape of a LAM-deficient mutant deforms due to the weakened cell wall will be tested. The potential molecular mechanism of LAM suppressing peptidoglycan hydrolases will be examined. In the second aim, the hypothesis that the morphological defect of the LAM-deficient mutant can be overcome by activating the SenX3-RegX3 two-component system and increas- ing the production of a-glucan will be examined. The proposed research is innovative because it reveals a new role of mycobacterial lipoglycans in maintaining glycan homeostasis, and because it combines the synergistic expertise of the applicant and his collaborators in forward genetics and bioorthogonal metabolic labeling of cell wall biosynthesis, a substantive departure from the status quo in both concept and execution. The proposed research is significant because the data obtained here will form the foundation for developing drugs that could kill M. tuberculosis by targeting a regulatory mechanism of mycobacterial cell envelope homeostasis. Such a drug may also make the cell envelope more permeable to other antimicrobials.