Taxonomic distribution of proteins containing UIM domains

The UIM domain within your query sequence starts at position 189 and ends at position 208, and its E-value is 3.05e1.

A Ubiquitin-interacting Motif (UIM) Is Essential for Eps15 and Eps15R Ubiquitination.

Klapisz E, Sorokina I, Lemeer S, Pijnenburg M, Verkleij AJ, Van Bergen En Henegouwen PM
J Biol Chem. 2002; 277: 30746-53

An important negative control mechanism in the signaling of epidermal growth factor (EGF) is the endocytosis and subsequent degradation of activated EGF receptors. Eps15 and its related partner Eps15R play a key role in clathrin-mediated endocytosis of transmembrane receptors. Upon EGF stimulation of the cell, Eps15 becomes both phosphorylated on tyrosine residues and monoubiquitinated. Although tyrosine phosphorylation of Eps15 has been implicated in EGF receptor internalization, the function of Eps15 ubiquitination is not known. Using a mutational approach, we have found that the second ubiquitin-interacting motif (UIM) of Eps15 and Eps15R is essential for their ubiquitination. This UIM partially overlaps with the recently characterized nuclear export signal in Eps15. We show that these two overlapping motifs have different structural requirements with respect to nuclear export signal versus ubiquitination signal activity. Our data demonstrate that the UIM does not contain the ubiquitin acceptor site but functions as a recruitment site for the ubiquitination machinery leading to the monoubiquitination of both Eps15 and Eps15R.

The ubiquitin-interacting motifs target the endocytic adaptor protein epsin for ubiquitination.

Oldham CE, Mohney RP, Miller SL, Hanes RN, O'Bryan JP
Curr Biol. 2002; 12: 1112-6

The covalent attachment of ubiquitin to proteins is an evolutionarily conserved signal for rapid protein degradation. However, additional cellular functions for ubiquitination are now emerging, including regulation of protein trafficking and endocytosis. For example, recent genetic studies suggested a role for ubiquitination in regulating epsin, a modular endocytic adaptor protein that functions in the assembly of clathrin-coated vesicles; however, biochemical evidence for this notion has been lacking. Epsin consists of an epsin NH(2)-terminal homology (ENTH) domain that promotes the interaction with phospholipids, several AP2 binding sites, two clathrin binding sequences, and several Eps15 homology (EH) domain binding motifs. Interestingly, epsin also possesses several recently described ubiquitin-interacting motifs (UIMs) that have been postulated to bind ubiquitin. Here, we demonstrate that epsin is predominantly monoubiquitinated and resistant to proteasomal degradation. The UIMs are necessary for epsin ubiquitination but are not the site of ubiquitination. Finally, we demonstrate that the isolated UIMs from both epsin and an unrelated monoubiquitinated protein, Eps15, are sufficient to promote ubiquitination of a chimeric glutathione-S-transferase (GST)-UIM fusion protein. Thus, our data suggest that UIMs may serve as a general signal for ubiquitination.

A single motif responsible for ubiquitin recognition and monoubiquitination in endocytic proteins.

Polo S, Sigismund S, Faretta M, Guidi M, Capua MR, Bossi G, Chen H, De Camilli P, Di Fiore PP
Nature. 2002; 416: 451-5

Ubiquitination is a post-translation modification in which ubiquitin chains or single ubiquitin molecules are appended to target proteins, giving rise to poly- or monoubiquitination, respectively. Polyubiquitination targets proteins for destruction by the proteasome. The role of monoubiquitination is less understood, although a function in membrane trafficking is emerging, at least in yeast. Here we report that a short amino-acid stretch at the carboxy-termini of the monoubiquitinated endocytic proteins Eps15 and eps15R is indispensable for their monoubiquitination. A similar sequence, also required for this modification, is found in other cytosolic endocytic proteins, such as epsins and Hrs. These sequences comprise a protein motif, UIM (ref. 6), which has been proposed to bind to ubiquitin. We confirm this for the UIMs of eps15, eps15R, epsins and Hrs. Thus, the same motif in several endocytic proteins is responsible for ubiquitin recognition and monoubiquitination. Our results predict the existence of a UIM:ubiquitin-based intracellular network. Eps15/eps15R, epsins and Hrs may function as adaptors between ubiquitinated membrane cargo and either the clathrin coat or other endocytic scaffolds. In addition, through their own ubiquitination, they may further contribute to the amplification of this network in the endocytic pathway.

RING for destruction?

Freemont PS
Curr Biol. 2000; 10: 847-847

Ubiquitination targets proteins for degradation and is a potent regulator of cellular protein function. Recent results implicate the RING finger domain in specific ubiquitination events; it is possible that all RING proteins act as E3 ubiquitin protein ligases, with implications for a variety of biological areas.

Interaction of hHR23 with S5a. The ubiquitin-like domain of hHR23 mediates interaction with S5a subunit of 26 S proteasome.

Hiyama H, Yokoi M, Masutani C, Sugasawa K, Maekawa T, Tanaka K, Hoeijmakers JH, Hanaoka F
J Biol Chem. 1999; 274: 28019-25

hHR23B is one of two human homologs of the Saccharomyces cerevisiae nucleotide excision repair (NER) gene product RAD23 and a component of a protein complex that specifically complements the NER defect of xeroderma pigmentosum group C (XP-C) cell extracts in vitro. Although a small proportion of hHR23B is tightly complexed with the XP-C responsible gene product, XPC protein, a vast majority exists as an XPC-free form, indicating that hHR23B has additional functions other than NER in vivo. Here we demonstrate that the human NER factor hHR23B as well as another human homolog of RAD23, hHR23A, interact specifically with S5a, a subunit of the human 26 S proteasome using the yeast two-hybrid system. Furthermore, hHR23 proteins were detected with S5a at the position where 26 S proteasome sediments in glycerol gradient centrifugation of HeLa S100 extracts. Intriguingly, hHR23B showed the inhibitory effect on the degradation of (125)I-lysozyme in the rabbit reticulocyte lysate. hHR23 proteins thus appear to associate with 26 S proteasome in vivo. From co-precipitation experiments using several series of deletion mutants, we defined the domains in hHR23B and S5a that mediate this interaction. From these results, we propose that part of hHR23 proteins are involved in the proteolytic pathway in cells.

Epsin is an EH-domain-binding protein implicated in clathrin-mediated endocytosis.

Chen H, Fre S, Slepnev VI, Capua MR, Takei K, Butler MH, DiFiore PP, DeCamilli P
Nature. 1998; 394: 793-7

During endocytosis, clathrin and the clathrin adaptor protein AP-2, assisted by a variety of accessory factors, help to generate an invaginated bud at the cell membrane. One of these factors is Eps15, a clathrin-coat-associated protein that binds the alpha-adaptin subunit of AP-2. Here we investigate the function of Eps15 by characterizing an important binding partner for its region containing EH domains; this protein, epsin, is closely related to the Xenopus mitotic phosphoprotein MP90 and has a ubiquitous tissue distribution. It is concentrated together with Eps15 in presynaptic nerve terminals, which are sites specialized for the clathrin-mediated endocytosis of synaptic vesicles. The central region of epsin binds AP-2 and its carboxy-terminal region binds Eps15. Epsin is associated with clathrin coats in situ, can be co-precipitated with AP-2 and Eps15 from brain extracts, but does not co-purify with clathrin coat components in a clathrin-coated vesicle fraction. When epsin function is disrupted, clathrin-mediated endocytosis is blocked. We propose that epsin may participate, together with Eps15, in the molecular rearrangement of the clathrin coats that are required for coated-pit invagination and vesicle fission.

VHS domain marks a group of proteins involved in endocytosis and vesicular trafficking.

Lohi O, Lehto VP
FEBS Lett. 1998; 440: 255-7

Endocytosis is driven by a mechanism which is characterized by an orderly congregation of a large number of proteins which effectuate, first, formation of a coated vesicles, second, pinching off the vesicle and, third, regulated transport. True to the nature of many other proteins involved in multimolecular complexes, also endocytosis-associated proteins, such as Eps15, clathrin and AP-2, are characterized by distinct domains which mediate the protein-protein interactions. We now report that a group of well-established endocytosis and/or vesicular trafficking proteins possess a VHS domain, a recently described domain with an unknown function. We suggest that in these proteins VHS serves as a membrane targeting domain which by its specific features together with FYVE, SH3 and/or TAM domains, which are also present in some VHS-containing proteins, is involved in the stage-specific assembly of the endocytic machinery.

Ubiquitin-dependent protein degradation.

Hochstrasser M
Annu Rev Genet. 1996; 30: 405-39

A growing number of cellular regulatory mechanisms are being linked to protein modification by the polypeptide ubiquitin. These include key transitions in the cell cycle, class I antigen processing, signal transduction pathways, and receptor-mediated endocytosis. In most, but not all, of these examples, ubiquitination of a protein leads to its degradation by the 26S proteasome. Following attachment of ubiquitin to a substrate and binding of the ubiquitinated protein to the proteasome, the bound substrate must be unfolded (and eventually deubiquitinated) and translocated through a narrow set of channels that leads to the proteasome interior, where the polypeptide is cleaved into short peptides. Protein ubiquitination and deubiquitination are both mediated by large enzyme families, and the proteasome itself comprises a family of related but functionally distinct particles. This diversity underlies both the high substrate specificity of the ubiquitin system and the variety of regulatory mechanisms that it serves.