CD9 is a gene encoding a protein that is a member of the transmembrane 4 superfamily also known as the tetraspanin family. It is a cell surface glycoprotein that consists of four transmembrane regions and has two extracellular loops that contain disulfide bonds which are conserved throughout the tetraspanin family.[5][6][7] Also containing distinct palmitoylation sites that allows CD9 to interact with lipids and other proteins.[5][8][9]
^Yáñez-Mó M, Barreiro O, Gordon-Alonso M, Sala-Valdés M, Sánchez-Madrid F (September 2009). "Tetraspanin-enriched microdomains: a functional unit in cell plasma membranes". Trends in Cell Biology. 19 (9): 434–46. doi:10.1016/j.tcb.2009.06.004. PMID19709882.