InterPro domain: IPR021648

Vps36 is a subunit of ESCRT-II, a protein complex involved in driving protein sorting from endosomes to lysosomes. The GLUE domain of Vps36 allows for a tight interaction to occur between the protein and Vps28, a subunit of ESCRT-I. This interaction is critical for ubiquitinated cargo progression from early to late endosomes [ 1 ].

The multivesicular body (MVB) protein-sorting pathway targets transmembraneproteins either for degradation or for function in the vacuole/lysosomes. Thesignal for entry into this pathway is monoubiquitination of protein cargo,which results in incorporation of cargo into luminal vesicles at lateendosomes. Another crucial player is phosphatidylinositol 3-phosphate(PtdINS(3)P), which is enriched on early endosomes and on the luminal vesiclesof MVBs. The ESCRT complexes are critical for MVB budding and sorting ofmonoubiquitinated cargo into the luminal vesicles. Various Ub-binding domains(UBDs), such as UIM, UEV and NZF are found in suchmachineries. The Vps 36 subunit of the ESCRT-II trafficking complex binds bothphosphoinositides and ubiquitin. All members of the Vps36 family contain adivergent GRAM/PH-like domain and yeast and some other fungi have one or twoNZF domains inserted in the GRAM/PH-like domain.

The N-terminal region of Vps36 (EAP45) has been named the GLUE (GRAM-like ubiquitin-binding in EAP45)domain. The GLUE domain acts as a central cog driving the endosomal ESCRTmachinery, through simultaneous interactions with PtdIns3P-containingmembranes, ubiquitin, and ESCRT-I. Like other known ubiquitin-binding domains,the GLUE domain interacts with the hydrophobic surface patch of ubiquitin. TheGLUE domain is the first ubiquitin-binding domain shown to bindphosphoinositides, and the ability of the same domain to bind both ubiquitinand a phosphoinositide opens interesting possibilities for coordination ofmembrane interactions and cargo recognition [ 2 , 3 , 3 , 4 , 5 ].

The GLUE domain has a split PH-domain fold with two curved beta sheets andone long alpha helix. The two sheets (beta1-beta4 and beta5-beta7) form a beta barrel-like structure, the C-terminal alpha helix is wedgedbetween the two beta sheets, covering a hydrophobic core. The Vps36 GLUEdomain binds PtdIns3P via a positively charged lipid binding pocket,delineated by the variable loops beta1/beta2, beta5/beta6 and beta7/alpha1, incontrast to the vast majority of characterised PH domains, which use adifferent lipid binding pocket [ 6 , 6 ].

1. ESCRT-I core and ESCRT-II GLUE domain structures reveal role for GLUE in linking to ESCRT-I and membranes. Cell 125, 99-111
2. Eap45 in mammalian ESCRT-II binds ubiquitin via a phosphoinositide-interacting GLUE domain. J. Biol. Chem. 280, 19600-6
3. Structural basis of ubiquitin recognition by mammalian Eap45 GLUE domain. Nat. Struct. Mol. Biol. 13, 1031-2
4. ESCRT complexes assembled and GLUEd. Structure 14, 631-2
5. Ubiquitin-binding domains. Biochem. J. 399, 361-72