title: Deubiquitinases sharpen substrate discrimination during membrane protein degradation from the ER.
abstract: Newly synthesized membrane proteins are queried by ubiquitin ligase complexes and triaged between degradative and nondegradative fates. The mechanisms that convert modest differences in substrate-ligase interactions into decisive outcomes of ubiquitination are not well understood. Here, we reconstitute membrane protein recognition and ubiquitination in liposomes using purified components from a viral-mediated degradation pathway. We find that substrate-ligase interactions in the membrane directly influence processivity of ubiquitin attachment to modulate polyubiquitination. Unexpectedly, differential processivity alone could not explain the differential fates in cultured cells of degraded and nondegraded clients. Both computational and experimental analyses identified continuous deubiquitination as a prerequisite for maximal substrate discrimination. Deubiquitinases reduce polyubiquitin dwell times preferentially on clients that dissociate more rapidly from the ligase. This explains how small differences in substrate-ligase interaction can be amplified into larger differences in net degradation. These results provide a conceptual framework for substrate discrimination during membrane protein quality control.
authors.affiliation: Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, 18 Library Drive, Bethesda, MD 20892, USA. zairong.zhang@gmail.com
authors.forename: Zai-Rong
authors.initials: ZR
authors.lastname: Zhang
authors.forename: Juan S
authors.initials: JS
authors.lastname: Bonifacino
authors.forename: Ramanujan S
authors.initials: RS
authors.lastname: Hegde
mesh_terms: D015704:CD4 Antigens / Q000737:chemistry / Q000378:metabolism; D010450:Endopeptidases / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D057809:HEK293 Cells; D006367:HeLa Cells; D054298:Human Immunodeficiency Virus Proteins / Q000378:metabolism; D006801:Humans; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D059748:Proteolysis; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D054875:Ubiquitination; D054334:Viral Regulatory and Accessory Proteins / Q000378:metabolism; D000086082:Viroporin Proteins
chemical_list: D015704:CD4 Antigens; D010450:Endopeptidases; D054298:Human Immunodeficiency Virus Proteins; D008081:Liposomes; D008565:Membrane Proteins; D046988:Proteasome Endopeptidase Complex; D044767:Ubiquitin-Protein Ligases; D054334:Viral Regulatory and Accessory Proteins; C514859:vpu protein, Human immunodeficiency virus 1; D000086082:Viroporin Proteins
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