TUG is a GLUT4 regulating protein and functions to retain membrane vesicles containing GLUT4 intracellularly. TUG releases the GLUT4 containing vesicles to the cellular exocytic machinery in response to insulin stimulation which allows translocation to the plasma membrane [1]. TUG has an N-terminal ubiquitin-like domain (UBL1) which in similar proteins appears to participate in protein-protein interactions [1]. The region does have a area of negative electrostatic potential and increased backbone motility which leads to suggestions of a potential protein-protein interaction site [1]. This domain is also found at the N-terminus of yeast UBX4 [2].

1: Solution structure and backbone dynamics of an N-terminal ubiquitin-like domain in the GLUT4-regulating protein, TUG. Tettamanzi MC, Yu C, Bogan JS, Hodsdon ME; Protein Sci. 2006;15:498-508. PMID:16501224

2: Ubx4 modulates cdc48 activity and influences degradation of misfolded proteins of the endoplasmic reticulum. Alberts SM, Sonntag C, Schafer A, Wolf DH; J Biol Chem. 2009;284:16082-16089. PMID:19359248