CD81

CD81 is a protein that in humans is encoded by the CD81 gene. It is also known as TAPA-1 (Target of the Antiproliferative Antibody 1) and TSPAN28 (Tetraspanin-28). CD81 is a member of the tetraspanin family, which are integral membrane proteins involved in several important biological processes.

Structure

CD81 is a cell surface protein that spans the membrane four times, hence the name tetraspanin. It has a small and a large extracellular loop, with the large loop being the primary site for antibody binding. The protein is 236 amino acids long and has a molecular weight of approximately 26 kDa.

Function

CD81 plays a crucial role in several cellular processes, including cell adhesion, cell motility, and cell proliferation. It is also involved in the regulation of B cell and T cell activation. CD81 interacts with other proteins, such as CD19, CD21, and MHC class II molecules, to form the B cell co-receptor complex, which plays a critical role in B cell activation and antibody production.

In addition to its role in immune cell function, CD81 is also a receptor for Hepatitis C virus (HCV). The virus binds to CD81 on the surface of hepatocytes, facilitating its entry into the cell.

Clinical significance

Given its role in HCV entry, CD81 is a potential target for antiviral therapies. Inhibiting the interaction between HCV and CD81 can prevent the virus from entering hepatocytes, thereby preventing infection.

Furthermore, alterations in CD81 expression have been associated with various diseases, including cancer. Overexpression of CD81 has been observed in several types of cancer, including breast cancer and melanoma, and is associated with increased cell motility and invasiveness.

See also

• Tetraspanin
• Hepatitis C virus
• B cell
• T cell
• Cancer