Tetraspannids

Tetraspannins are a superfamily of transmembrane proteins found in the plasma membrane and intracellular organelles of eukaryotic cells. They are characterized by a conserved structure that includes four transmembrane domains, two extracellular loops, and two short intracellular loops, along with N- and C-terminal tails that face the cytoplasm. This structural motif has led to their name, "tetraspannins," which means "four spans."

These proteins are highly abundant and diverse, with approximately 30 known tetraspannins in mammals. They do not possess intrinsic enzymatic activity themselves but play crucial roles in cell biology by organizing and stabilizing protein complexes within the cell membrane. They act as scaffolds, bringing together a variety of other membrane proteins, including integrins, growth factor receptors, and other tetraspannins, into functional microdomains.

The precise functions of tetraspannins are varied and context-dependent, often influenced by the specific tetraspannin and the cell type in which it is expressed. They are involved in a wide range of cellular processes such as cell adhesion, cell migration, cell proliferation, immune cell activation, and viral entry. Their ability to modulate the activity and localization of other membrane proteins makes them key regulators of cellular signaling pathways. Due to their diverse roles in cell function and their involvement in various diseases, including cancer and infectious diseases, tetraspannins are an active area of research.