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Concept
Mannose receptor
Résumé
The mannose receptor (Cluster of Differentiation 206, CD206) is a C-type lectin primarily present on the surface of macrophages, immature dendritic cells and liver sinusoidal endothelial cells, but is also expressed on the surface of skin cells such as human dermal fibroblasts and keratinocytes. It is the first member of a family of endocytic receptors that includes Endo180 (CD280), M-type PLA2R, and DEC-205 (CD205).
The receptor recognises terminal mannose, N-acetylglucosamine and fucose residues on glycans attached to proteins found on the surface of some microorganisms, playing a role in both the innate and adaptive immune systems. Additional functions include clearance of glycoproteins from circulation, including sulphated glycoprotein hormones and glycoproteins released in response to pathological events. The mannose receptor recycles continuously between the plasma membrane and endosomal compartments in a clathrin-dependent manner.
The mannose receptor is a type I transmembrane protein, with an extracellular N-terminus and an intracellular C-terminus. It is first synthesised as an inactive precursor, but is proteolytically cleaved to its active form in the Golgi apparatus. In general, The extracellular portion of the receptor is composed of 8 consecutive C-type carbohydrate recognition domains (CRDs) closest to the plasma membrane, followed by a single fibronectin type II repeat domain and an N-terminal cysteine-rich domain. The cytoplasmic tail is not capable of signal transduction in isolation, since it lacks the appropriate signaling motifs.
The N-terminal cysteine-rich domain is homologous to the ricin B chain and binds to sulphated sugar moieties, with particularly high affinity for N-Acetylgalactosamine and galactose residues sulphated at positions 3 and 4 of their pyranose rings.
Other ligands include chondroitin sulfates A and B, as well as sulphated Lewisx and Lewisa structures. The mannose receptor is the only member of the family in which this domain is functional.
Source officielle
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