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From Proteopedia
SLC15A4_TASL complex
Structural highlights
FunctionS15A4_HUMAN Proton-coupled amino-acid transporter that mediates the transmembrane transport of L-histidine and some di- and tripeptides from inside the lysosome to the cytosol, and plays a key role in innate immune response (PubMed:16289537, PubMed:25238095, PubMed:29224352). Able to transport a variety of di- and tripeptides, including carnosine and some peptidoglycans (PubMed:29224352, PubMed:31073693). Transporter activity is pH-dependent and maximized in the acidic lysosomal environment (By similarity). Involved in the detection of microbial pathogens by toll-like receptors (TLRs) and NOD-like receptors (NLRs), probably by mediating transport of bacterial peptidoglycans across the endolysosomal membrane: catalyzes the transport of certain bacterial peptidoglycans, such as muramyl dipeptide (MDP), the NOD2 ligand, and L-alanyl-gamma-D-glutamyl-meso-2,6-diaminoheptanedioate (tri-DAP), the NOD1 ligand (PubMed:25238095, PubMed:29224352). Required for TLR7, TLR8 and TLR9-mediated type I interferon (IFN-I) productions in plasmacytoid dendritic cells (pDCs) (PubMed:25238095). Independently of its transporter activity, also promotes the recruitment of innate immune adapter TASL to endolysosome downstream of TLR7, TLR8 and TLR9: TASL recruitment leads to the specific recruitment and activation of IRF5 (PubMed:32433612). Required for isotype class switch recombination to IgG2c isotype in response to TLR9 stimulation (By similarity). Required for mast cell secretory-granule homeostasis by limiting mast cell functions and inflammatory responses (By similarity).[UniProtKB:O09014][UniProtKB:Q91W98][1] [2] [3] [4] [5] Publication Abstract from PubMedToll-like receptors (TLRs) are a class of proteins that play critical roles in recognizing pathogens and initiating innate immune responses. TASL, a recently identified innate immune adaptor protein for endolysosomal TLR7/8/9 signaling, is recruited by the lysosomal proton-coupled amino-acid transporter SLC15A4, and then activates IRF5, which in turn triggers the transcription of type I interferons and cytokines. Here, we report three cryo-electron microscopy (cryo-EM) structures of human SLC15A4 in the apo monomeric and dimeric state and as a TASL-bound complex. The apo forms are in an outward-facing conformation, with the dimeric form showing an extensive interface involving four cholesterol molecules. The structure of the TASL-bound complex reveals an unprecedented interaction mode with solute carriers. During the recruitment of TASL, SLC15A4 undergoes a conformational change from an outward-facing, lysosomal lumen-exposed state to an inward-facing state to form a binding pocket, allowing the N-terminal helix of TASL to be inserted into. Our findings provide insights into the molecular basis of regulatory switch involving a human solute carrier and offers an important framework for structure-guided drug discovery targeting SLC15A4-TASL-related human autoimmune diseases. Structural basis for recruitment of TASL by SLC15A4 in human endolysosomal TLR signaling.,Chen X, Xie M, Zhang S, Monguio-Tortajada M, Yin J, Liu C, Zhang Y, Delacretaz M, Song M, Wang Y, Dong L, Ding Q, Zhou B, Tian X, Deng H, Xu L, Liu X, Yang Z, Chang Q, Na J, Zeng W, Superti-Furga G, Rebsamen M, Yang M Nat Commun. 2023 Oct 20;14(1):6627. doi: 10.1038/s41467-023-42210-9. PMID:37863913[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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