title: Endoplasmic reticulum-associated degradation of a degron-containing polytopic membrane protein.
abstract: The presence of two basic amino acids strategically located within a single spanning transmembrane region has previously been shown to act as a signal for the endoplasmic reticulum associated degradation (ERAD) of several polypeptides. In contrast, the functionality of this degron motif within the context of a polytopic membrane protein has not been established. Using opsin as a model system, we have investigated the consequences of inserting the degron motif in the first of its seven transmembrane (TM) spans. Whilst these basic residue reduce the binding of the targeting factor, signal recognition particle, to the first TM span, this has no effect on membrane integration in vitro or in vivo. This most likely reflects the presence of multiple TM spans that can act as targeting signals within in the nascent opsin chain. We find that the degron motif leads to the efficient retention of mutant opsin chains at the endoplasmic reticulum. The mutant opsin polypeptides are degraded via a proteasomal pathway that involves the actions of the E3 ubiquitin ligase HRD1. In contrast, wild-type opsin remains stable for a prolonged period even when artificially accumulated at the endoplasmic reticulum. We conclude that a single dibasic degron motif is sufficient to initiate both the ER retention and subsequent degradation of ospin via an ERAD pathway.
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, UK.
authors.forename: Arpita
authors.initials: A
authors.lastname: Ray-Sinha
authors.forename: Benedict C S
authors.initials: BC
authors.lastname: Cross
authors.forename: Aleksandr
authors.initials: A
authors.lastname: Mironov
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Wiertz
authors.forename: Stephen
authors.initials: S
authors.lastname: High
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D002417:Cattle; D004721:Endoplasmic Reticulum / Q000502:physiology*; D008565:Membrane Proteins / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D055355:Opsins / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D055550:Protein Stability
chemical_list: D008565:Membrane Proteins; D055355:Opsins; D046988:Proteasome Endopeptidase Complex