Tetraspanin, extracellular domain or large extracellular loop (LEL), CD37_CD82_Like 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". CD37 is a leukocyte-specific protein, and its restricted expression pattern suggests a role in the immune system. A regulatory role in T-cell proliferation has been suggested. CD82 is a metastasis suppressor implicated in biological processes ranging from fusion, adhesion, and migration to apoptosis and alterations of cell morphology.
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