title: dPob/EMC is essential for biosynthesis of rhodopsin and other multi-pass membrane proteins in Drosophila photoreceptors.
abstract: In eukaryotes, most integral membrane proteins are synthesized, integrated into the membrane, and folded properly in the endoplasmic reticulum (ER). We screened the mutants affecting rhabdomeric expression of rhodopsin 1 (Rh1) in the Drosophila photoreceptors and found that dPob/EMC3, EMC1, and EMC8/9, Drosophila homologs of subunits of ER membrane protein complex (EMC), are essential for stabilization of immature Rh1 in an earlier step than that at which another Rh1-specific chaperone (NinaA) acts. dPob/EMC3 localizes to the ER and associates with EMC1 and calnexin. Moreover, EMC is required for the stable expression of other multi-pass transmembrane proteins such as minor rhodopsins Rh3 and Rh4, transient receptor potential, and Na(+)K(+)-ATPase, but not for a secreted protein or type I single-pass transmembrane proteins. Furthermore, we found that dPob/EMC3 deficiency induces rhabdomere degeneration in a light-independent manner. These results collectively indicate that EMC is a key factor in the biogenesis of multi-pass transmembrane proteins, including Rh1, and its loss causes retinal degeneration.
authors.affiliation: Graduate School of Integrated Arts and Science, Hiroshima University, Higashi-Hiroshima, Japan.
authors.forename: Takunori
authors.initials: T
authors.lastname: Satoh
authors.affiliation: Graduate School of Integrated Arts and Science, Hiroshima University, Higashi-Hiroshima, Japan.
authors.forename: Aya
authors.initials: A
authors.lastname: Ohba
authors.affiliation: Institute of Animal Husbandry, Heilongjiang Academy of Agricultural Sciences, Harbin, China.
authors.forename: Ziguang
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Graduate School of Integrated Arts and Science, Hiroshima University, Higashi-Hiroshima, Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Inagaki
authors.affiliation: Graduate School of Integrated Arts and Science, Hiroshima University, Higashi-Hiroshima, Japan.
authors.forename: Akiko K
authors.initials: AK
authors.lastname: Satoh
mesh_terms: D000818:Animals; D004330:Drosophila / Q000378:metabolism*; D029721:Drosophila Proteins / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D017956:Photoreceptor Cells, Invertebrate / Q000378:metabolism*; D021381:Protein Transport; D012243:Rhodopsin / Q000096:biosynthesis*
chemical_list: D029721:Drosophila Proteins; D008565:Membrane Proteins; D012243:Rhodopsin
keywords: D. melanogaster; EMC; cell biology; chaperon; rhodopsin; transmembrane protein