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Heterotrimeric Complex of Human ASCT2 with Syncytin-1
Structural highlights
FunctionAAAT_HUMAN Sodium-dependent amino acids transporter that has a broad substrate specificity, with a preference for zwitterionic amino acids. It accepts as substrates all neutral amino acids, including glutamine, asparagine, and branched-chain and aromatic amino acids, and excludes methylated, anionic, and cationic amino acids (PubMed:8702519). Through binding of the fusogenic protein syncytin-1/ERVW-1 may mediate trophoblasts syncytialization, the spontaneous fusion of their plasma membranes, an essential process in placental development (PubMed:10708449, PubMed:23492904).[1] [2] [3] (Microbial infection) Acts as a cell surface receptor for Feline endogenous virus RD114.[4] [5] (Microbial infection) Acts as a cell surface receptor for Baboon M7 endogenous virus.[6] (Microbial infection) Acts as a cell surface receptor for type D simian retroviruses.[7] Publication Abstract from PubMedHuman syncytin-1 and suppressyn are cellular proteins of retroviral origin involved in cell-cell fusion events to establish the maternal-fetal interface in the placenta. In cell culture, they restrict infections from members of the largest interference group of vertebrate retroviruses, and are regarded as host immunity factors expressed during development. At the core of the syncytin-1 and suppressyn functions are poorly understood mechanisms to recognize a common cellular receptor, the membrane transporter ASCT2. Here, we present cryo-electron microscopy structures of human ASCT2 in complexes with the receptor-binding domains of syncytin-1 and suppressyn. Despite their evolutionary divergence, the two placental proteins occupy similar positions in ASCT2, and are stabilized by the formation of a hybrid beta-sheet or 'clamp' with the receptor. Structural predictions of the receptor-binding domains of extant retroviruses indicate overlapping binding interfaces and clamping sites with ASCT2, revealing a competition mechanism between the placental proteins and the retroviruses. Our work uncovers a common ASCT2 recognition mechanism by a large group of endogenous and disease-causing retroviruses, and provides high-resolution views on how placental human proteins exert morphological and immunological functions. Receptor-recognition and antiviral mechanisms of retrovirus-derived human proteins.,Khare S, Villalba MI, Canul-Tec JC, Cajiao AB, Kumar A, Backovic M, Rey FA, Pardon E, Steyaert J, Perez C, Reyes N Nat Struct Mol Biol. 2024 Sep;31(9):1368-1376. doi: 10.1038/s41594-024-01295-6. , Epub 2024 Apr 26. PMID:38671230[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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