3p7f
From Proteopedia
Structure of the human Langerin carbohydrate recognition domain
Structural highlights
DiseaseCLC4K_HUMAN Defects in CD207 are the cause of Birbeck granule deficiency (BIRGD) [MIM:613393. It is a condition characterized by the absence of Birbeck granules in epidermal Langerhans cells. Despite the lack of Birbeck granules Langerhans cells are present in normal numbers and have normal morphologic characteristics and antigen-presenting capacity.[1] [2] FunctionCLC4K_HUMAN Calcium-dependent lectin displaying mannose-binding specificity. Induces the formation of Birbeck granules (BGs); is a potent regulator of membrane superimposition and zippering. Binds to sulfated as well as mannosylated glycans, keratan sulfate (KS) and beta-glucans. Facilitates uptake of antigens and is involved in the routing and/or processing of antigen for presentation to T cells. Major receptor on primary Langerhans cells for Candida species, Saccharomyces species, and Malassezia furfur. Protects against human immunodeficiency virus-1 (HIV-1) infection. Binds to high-mannose structures present on the envelope glycoprotein which is followed by subsequent targeting of the virus to the Birbeck granules leading to its rapid degradation.[3] [4] [5] [6] Publication Abstract from PubMedLangerin is a type II transmembrane oligosaccharide receptor on Langerhans cells (LCs), a prominent subclass of dendritic cells (DCs) that mediate immune responses in epithelia and play a role in HIV degradation. Its extracellular moiety comprises a neck region with several heptad repeats and an exposed carboxy-terminal calcium-type carbohydrate-recognition domain (CRD). The CRD of human Langerin, which was expressed as a soluble protein in the periplasm of E. coli, was crystallized both alone and in the presence of two sugars, followed by X-ray analyses to resolutions of 2.5A for apo-Langerin and to 1.6A and 2.1A for the complexes with mannose and maltose, respectively. The fold of the Langerin CRD (dubbed LangA) resembles that of other typical C-type lectins such as DC-SIGN. However, especially in the long loop region (LLR), which is responsible for carbohydrate-binding, two additional secondary structure elements are present: a 3(10) helix and a small beta-sheet arising from the extended beta-strand 2, which enters into a hairpin and a new strand beta2'. Unexpectedly, the crystal structures in the presence of maltose and mannose reveal two sugar-binding sites. One is calcium-dependent and structurally conserved in the C-type lectin family whereas the second one represents a novel, calcium-independent type. Based on these data, a model for the binding of mannan, a component of many endogenous as well as viral glycoproteins, is proposed and the differences in binding behavior between Langerin and DC-SIGN with respect to the Lewis X carbohydrate antigen and its derivatives can be explained. Therefore, the crystal structure of LangA should be helpful for the development of new marker reagents selective for LCs and also of therapeutic compounds that may enhance the inhibitory role of Langerin towards HIV infection. The carbohydrate recognition domain of Langerin reveals high structural similarity with the one of DC-SIGN but an additional, calcium-independent sugar-binding site.,Chatwell L, Holla A, Kaufer BB, Skerra A Mol Immunol. 2008 Apr;45(7):1981-94. Epub 2007 Dec 3. PMID:18061677[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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