Ubiquitin-interacting motif


In molecular biology, the Ubiquitin-Interacting Motif, or 'LALAL-motif', is a sequence motif of about 20 amino acid residues, which was first described in the 26S proteasome subunit PSD4/RPN-10 that is known to recognise ubiquitin. In addition, the UIM is found, often in tandem or triplet arrays, in a variety of proteins either involved in ubiquitination and ubiquitin metabolism, or known to interact with ubiquitin-like modifiers. Among the UIM proteins are two different subgroups of the UBP family of deubiquitinating enzymes, one F-box protein, one family of HECT-containing ubiquitin-ligases from plants, and several proteins containing ubiquitin-associated UBA and/or UBX domains. In most of these proteins, the UIM occurs in multiple copies and in association with other domains such as UBA, UBX, ENTH domain, EH, VHS, SH3 domain, HECT, VWFA, EF-hand calcium-binding, WD-40, F-box, LIM, protein kinase, ankyrin, PX, phosphatidylinositol 3- and 4-kinase, C2 domain, OTU, DnaJ domain, RING-finger or FYVE-finger. UIMs have been shown to bind ubiquitin and to serve as a specific targeting signal important for monoubiquitination. Thus, UIMs may have several functions in ubiquitin metabolism each of which may require different numbers of UIMs.
The UIM is unlikely to form an independent protein domain. Instead, based on the spacing of the conserved residues, the motif probably forms a short alpha-helix that can be embedded into different protein folds. Some proteins known to contain an UIM are listed below: