title: Transmembrane domain quality control systems operate at the endoplasmic reticulum and Golgi apparatus.
abstract: Multiple protein quality control systems operate to ensure that misfolded proteins are efficiently cleared from the cell. While quality control systems that assess the folding status of soluble domains have been extensively studied, transmembrane domain (TMD) quality control mechanisms are poorly understood. Here, we have used chimeras based on the type I plasma membrane protein CD8 in which the endogenous TMD was substituted with transmembrane sequences derived from different polytopic membrane proteins as a mode to investigate the quality control of unassembled TMDs along the secretory pathway. We find that the three TMDs examined prevent trafficking of CD8 to the cell surface via potentially distinct mechanisms. CD8 containing two distinct non-native transmembrane sequences escape the ER and are subsequently retrieved from the Golgi, possibly via Rer1, leading to ER localisation at steady state. A third chimera, containing an altered transmembrane domain, was predominantly localised to the Golgi at steady state, indicating the existence of an additional quality control checkpoint that identifies non-native transmembrane domains that have escaped ER retention and retrieval. Preliminary experiments indicate that protein retained by quality control mechanisms at the Golgi are targeted to lysosomes for degradation.
authors.affiliation: Division of Molecular and Cellular Function, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester Academic Health Science Centre, Manchester, United Kingdom.
authors.forename: Kit
authors.initials: K
authors.lastname: Briant
authors.affiliation: Division of Molecular and Cellular Function, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester Academic Health Science Centre, Manchester, United Kingdom.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Johnson
authors.affiliation: Division of Molecular and Cellular Function, School of Biological Sciences, Faculty of Biology, Medicine and Health, University of Manchester, Manchester Academic Health Science Centre, Manchester, United Kingdom.
authors.forename: Eileithyia
authors.identifier: http://orcid.org/0000-0002-3299-4228
authors.initials: E
authors.lastname: Swanton
mesh_terms: D000818:Animals; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D011786:Quality Control