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Tetraspanin, extracellular domain or large extracellular loop (LEL), CD63 family. Tetraspanins are trans-membrane proteins with 4 trans-membrane segments. Both the N- and C-termini lie on the intracellular side of the membrane. This alignment model spans the extracellular domain between the 3rd and 4th trans-membrane segment. Tetraspanins are involved in diverse processes and their various functions may relate to their ability to act as molecular facilitators. Tetraspanins associate laterally with one another and cluster dynamically with numerous parnter domains in membrane microdomains, forming a network of multimolecular complexes, the "tetraspanin web". CD63 is present in platelets, neutrophils, and endothelial cells, amongst others. In platelets it associates with the integrin alphaIIBbeta3 and may modulate alphaIIbbeta3-dependent cytoskeletal reorganization.
Jiyao W et al.(2023). "The conserved domain database in 2023.",