CD81 (Cluster of Differentiation 81)

Abstract

Cluster of differentiation (CD81) is a type of protein, which is encoded by CD81 gene. Beside that CD81 is also known under other names such as Target of the Antiproliferative Antibody 1 (TAPA-1) and Tetraspanin-28 (TSPAN28). Location of CD81 is known to be on chromosome 11 (11p15.5), where it contains 15-20 bases in length. It is expressed mostly in cells of testis, ovary, endometrium, placenta, bone marrow, smooth muscles and others. The main function of the CD81 protein is to mediate signal transduction events, which are important for cells' development, activation, growth and motility. The CD81 gene is also known as a candidate for many malignancies because of its location. The characteristic feature of CD81 is that it is highly hydrophobic and contains a short N- and C-terminal cytoplasmic domains together with cytoplasmic cysteines, potential sites of palmitoylation as well as four transmembrane domains where they together hold the protein in a cell membrane. There are two CD81 isoforms, isoform 1 and isoform 2. Isoforms of CD81 are usually found in a tumor-suppressor region where they have a great impact on tumor development. There has always been a high interest in research on CD81 function in viral disease development. In fact, it is known that CD81 contributes in the development of diseases such as hepatitis C, malaria and various types of cancer. Since the complete effect of CD81 is unknown, further research and scientific methodology could potentially discover all possible functions and mechanisms regulated by the CD81 protein in human body.