Ubiquitin signals are decoded in cells by at least 200 ubiquitin binding proteins, which interact with different types of polyubiquitin chains and ubiquitin-like modifiers. These interactions induce conformational changes that allow these proteins to transmit the ubiquitin signal to effector proteins (Dikic et al., 2009). Cloning of the human Target Of Myb1 (TOM1) was first described by Seroussi et al. (1999). Human TOM1 shares 76% amino acid sequence identity with chicken TOM1 and 89% identity with mouse TOM1 (Seroussi, et al., 1999). The N-terminal domain of human TOM1 shares sequence similarity to the N-terminal domains of human Signal Transducing Adaptor Molecule (STAM) and Human Growth factor-regulated tyrosine kinase Substrate (HGS) (Seroussi, et al., 1999). TOM1 links polyubiquitin chains to Clathrin (Yamakami, et al., 2003). TOM1 has been shown to bind to human Toll-interacting protein (TOLLIP) via its GAT domain, TOM1 also interacts with Clathrin and when TOM1 and TOLLIP are co-expressed Clathrin is recruited to the endosome suggesting that they may modulate endosomal function (Katoh, et al., 2006). TOM1 directly associates with TOLLIP to form a complex, in which both TOM1 and TOLLIP are capable of directly binding polyubiquitin chains. It is thought that TOM1 is involved in the intracellular sorting of ubiquitylated proteins, analysis of the crystal structure of the TOM1-GAT domain with ubiquitin has revealed the presence of two ubiquitin binding domains (Akutsu, et al., 2005).
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