CD137/4-1BB/TNFRSF9 [4-1BB/4552R]

CD137 or 4-1BB is an inducible receptor-like protein expressed on the cell surface of activated splenic T cells and thymocytes. It exists as both a monomer and a dimer on the surface of activated T cells. 4-1BB is structurally related to the members of NGFR/TNFR superfamily which are characterized by the presence of three-six patterns of a cysteine-rich motif in their extracellular domains. Other members of this family include low affinity NGFR, two receptors for TNF (TNFR-I and TNFR-II), CD30, CD40, OX40, Fas, and CD27. These molecules are involved in cell growth, survival, and death processes. The cytoplasmic domain of 4-1BB include two runs of acidic amino acids, a potential p56lck binding site, five consecutive glycines at the C-terminus, and four potential phosphorylation sites: one tyrosine, two threonine, and one serine.