title: Eap45 in mammalian ESCRT-II binds ubiquitin via a phosphoinositide-interacting GLUE domain.
abstract: Ubiquitination serves as a key sorting signal in the lysosomal degradation of endocytosed receptors through the ability of ubiquitinated membrane proteins to be recognized and sorted by ubiquitin-binding proteins along the endocytic route. The ESCRT-II complex in yeast contains one such protein, Vps36, which harbors a ubiquitin-binding NZF domain and is required for vacuolar sorting of ubiquitinated membrane proteins. Surprisingly, the presumptive mammalian ortholog Eap45 lacks the ubiquitin-binding module of Vps36, and it is thus not clear whether mammalian ESCRT-II functions to bind ubiquitinated cargo. In this paper, we provide evidence that Eap45 contains a novel ubiquitin-binding domain, GLUE (GRAM-like ubiquitin-binding in Eap45), which binds ubiquitin with similar affinity and specificity as other ubiquitin-binding domains. The GLUE domain shares similarities in its primary and predicted secondary structures to phosphoinositide-binding GRAM and PH domains. Accordingly, we find that Eap45 binds to a subset of 3-phosphoinositides, suggesting that ubiquitin recognition could be coordinated with phosphoinositide binding. Furthermore, we show that Eap45 colocalizes with ubiquitinated proteins on late endosomes. These results are consistent with a role for Eap45 in endosomal sorting of ubiquitinated cargo.
authors.affiliation: Department of Biochemistry, The Norwegian Radium Hospital, Montebello, Oslo.
authors.forename: Thomas
authors.initials: T
authors.lastname: Slagsvold
authors.forename: Rein
authors.initials: R
authors.lastname: Aasland
authors.forename: Satoshi
authors.initials: S
authors.lastname: Hirano
authors.forename: Kristi G
authors.initials: KG
authors.lastname: Bache
authors.forename: Camilla
authors.initials: C
authors.lastname: Raiborg
authors.forename: Daniel
authors.initials: D
authors.lastname: Trambaiolo
authors.forename: Soichi
authors.initials: S
authors.lastname: Wakatsuki
authors.forename: Harald
authors.initials: H
authors.lastname: Stenmark
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D056827:Endosomal Sorting Complexes Required for Transport; D011992:Endosomes / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D033921:Vesicular Transport Proteins
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D026901:Membrane Transport Proteins; D046912:Multiprotein Complexes; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D025801:Ubiquitin; D033921:Vesicular Transport Proteins; C491128:Vps36 protein, S cerevisiae