Gilleron, M. | bioRxiv Science

bioRxiv2022

From Molecular Dynamics to Supramolecular Organization: The Role of PIM Lipids in the Originality of the Mycobacterial Plasma Membrane

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis, a disease that claims ~1.5 million lives annually. The current treatment regime is long and expensive, and missed doses contribute to drug resistance. There is much to be understood about the Mtb cell envelope, a complicated barrier that antibiotics need to negotiate to enter the cell. Within this envelope, the plasma membrane is the ultimate obstacle and is proposed to be comprised of over 50% mannosylated phosphatidylinositol lipids (phosphatidyl-myoinositol mannosides, PIMs), whose role in the membrane structure remains elusive. Here we used multiscale molecular dynamics (MD) simulations to understand the structure-function relationship of the PIM lipid family and decipher how they self-organize to drive biophysical properties of the Mycobacterial plasma membrane. To validate the model, we tested known anti-tubercular drugs and replicated previous experimental results. Our results shed new light into the organization of the Mycobacterial plasma membrane and provides a working model of this complex membrane to use for in silico studies. This opens the door for new methods to probe potential antibiotic targets and further understand membrane protein function. O_FIG O_LINKSMALLFIG WIDTH=169 HEIGHT=200 SRC="FIGDIR/small/498153v1_ufig1.gif" ALT="Figure 1"> View larger version (56K): org.highwire.dtl.DTLVardef@102b357org.highwire.dtl.DTLVardef@4c30f8org.highwire.dtl.DTLVardef@22f32aorg.highwire.dtl.DTLVardef@8a6f65_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2020

CD4 and CD8 co-receptors modulate functional avidity of CD1b-restricted T cells.

CD4 and CD8 co-receptors define distinct lineages of T cells restricted by major histocompatibility complex (MHC) Class II and I molecules, respectively. Co-receptors interact with the T cell receptor (TCR) at the surface of MHC-restricted T cells to facilitate antigen recognition, thymic selection, and functional differentiation. T cells also recognize lipid antigens presented by CD1 molecules, but the role that CD4 and CD8 play in lipid antigen recognition is unknown. We studied the effect of CD4 and CD8 on the avidity, activation, and function of T cells specific for two CD1b-presented mycobacterial lipid antigens, glucose monomycolate (GMM) and diacylated sulfoglycolipids (SGL). In a human cohort study using SGL-loaded CD1b tetramers, we discovered a hierarchy among SGL-specific T cells in which T cells expressing the CD4 or CD8 co-receptor stain with a higher tetramer mean fluorescence intensity (MFI) than CD4-CD8- T cells. To determine the role of the TCR co-receptor in lipid antigen recognition, we exogenously expressed GMM and SGL-specific TCRs in Jurkat or polyclonal T cells and quantified tetramer staining and activation thresholds. Transduced CD4+ primary T cells bound the lipid-loaded CD1b tetramer with a higher MFI than CD8+ primary T cells, and transduced CD8+ Jurkat cells bound the SGL-CD1b tetramer with higher MFI than CD4-CD8- Jurkat cells. The presence of either co-receptor also decreased the threshold for IFN-{gamma} secretion. Further, co-receptor expression increased surface expression of CD3{varepsilon}, suggesting a mechanism for increased tetramer binding and activation. Finally, we used single-cell sequencing to define the TCR repertoire and ex vivo functional profiles of SGL-specific T cells from individuals with M.tb disease. We found that CD8+ T cells specific for SGL express canonical markers associated with cytotoxic T lymphocytes, while CD4+ T cells could be classified as T regulatory or T follicular helper cells. Among SGL-specific T cells, only those expressing the CD4 co-receptor also expressed Ki67, suggesting that they were actively proliferating at the time of sample collection. Together, these data reveal that expression of CD4 and CD8 co-receptor modulates TCR avidity for lipid antigen, leading to functional diversity and differences in in vivo proliferation during M.tb disease.

immunology↗