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CRYSTAL STRUCTURE OF THE CARBOHYDRATE RECOGNITION DOMAIN OF THE H1 SUBUNIT OF THE ASIALOGLYCOPROTEIN RECEPTOR
Structural highlights
FunctionASGR1_HUMAN Mediates the endocytosis of plasma glycoproteins to which the terminal sialic acid residue on their complex carbohydrate moieties has been removed. The receptor recognizes terminal galactose and N-acetylgalactosamine units. After ligand binding to the receptor, the resulting complex is internalized and transported to a sorting organelle, where receptor and ligand are disassociated. The receptor then returns to the cell membrane surface. Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe human asialoglycoprotein receptor (ASGPR), also called hepatic lectin, is an integral membrane protein and is responsible for the clearance of desialylated, galactose-terminal glycoproteins from the circulation by receptor-mediated endocytosis. It can be subdivided into four functional domains: the cytosolic domain, the transmembrane domain, the stalk and the carbohydrate recognition domain (CRD). The galactose-binding domains belong to the superfamily of C-type (calcium-dependent) lectins, in particular to the long-form subfamily with three conserved intramolecular disulphide bonds. It is able to bind terminal non-reducing galactose residues and N-acetyl-galactosamine residues of desialated tri or tetra-antennary N-linked glycans. The ASGPR is a potential liver-specific receptor for hepatitis B virus and Marburg virus and has been used to target exogenous molecules specifically to hepatocytes for diagnostic and therapeutic purposes.Here, we present the X-ray crystal structure of the carbohydrate recognition domain of the major subunit H1 at 2.3 A resolution. While the overall fold of this and other known C-type lectin structures are well conserved, the positions of the bound calcium ions are not, indicating that the fold is stabilised by alternative mechanisms in different branches of the C-type lectin family. It is the first CRD structure where three calcium ions form an intergral part of the structure. In addition, the structure provides direct confirmation for the conversion of the ligand-binding site of the mannose-binding protein to an asialoglycoprotein receptor-like specificity suggested by Drickamer and colleagues. In agreement with the prediction that the coiled-coil domain of the ASGPR is separated from the CRD and its N-terminal disulphide bridge by several residues, these residues are indeed not alpha-helical, while in tetranectin they form an alpha-helical coiled-coil. Crystal structure of the carbohydrate recognition domain of the H1 subunit of the asialoglycoprotein receptor.,Meier M, Bider MD, Malashkevich VN, Spiess M, Burkhard P J Mol Biol. 2000 Jul 21;300(4):857-65. PMID:10891274[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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