title: MAG2 and three MAG2-INTERACTING PROTEINs form an ER-localized complex to facilitate storage protein transport in Arabidopsis thaliana.
abstract: In Arabidopsis thaliana, MAIGO 2 (MAG2) is involved in protein transport between the endoplasmic reticulum (ER) and the Golgi apparatus via its association with the ER-localized t-SNARE components SYP81/AtUfe1 and SEC20. To characterize the molecular machinery of MAG2-mediated protein transport, we explored MAG2-interacting proteins using transgenic A. thaliana plants expressing TAP-tagged MAG2. We identified three proteins, which were designated as MAG2-INTERACTING PROTEIN 1-3 [MIP1 (At2g32900), MIP2 (At5g24350) and MIP3 (At2g42700)]. Both MIP1 and MAG2 localized to the ER membrane. All of the mag2, mip1, mip2 and mip3 mutants exhibited a defect in storage protein maturation, and developed abnormal storage protein body (MAG body) structures in the ER of seed cells. These observations suggest that MIPs are closely associated with MAG2 and function in protein transport between the ER and Golgi apparatus. MIP1 and MIP2 contain a Zeste-White 10 (ZW10) domain and a Sec39 domain, respectively, but have low sequence identities (21% and 23%) with respective human orthologs. These results suggest that the plant MAG2-MIP1-MIP2 complex is a counterpart of the triple-subunit tethering complexes in yeast (Tip20p-Dsl1p-Sec39p) and humans (RINT1-ZW10-NAG). Surprisingly, the plant complex also contained a fourth member (MIP3) with a Sec1 domain. There have been no previous reports showing that a Sec1-containing protein is a subunit of ER-localized tethering complexes. Our results suggest that MAG2 and the three MIP proteins form a unique complex on the ER that is responsible for efficient transport of seed storage proteins.
authors.affiliation: Alkali Soil Natural Environmental Science Center, Key Laboratory of Saline-Alkali Vegetation Ecology Restoration in Oil Field (SAVER), Ministry of Education, Northeast Forestry University, Harbin, 150040, China; Department of Botany, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan; College of Life Science, Northeast Forestry University, Harbin, 150040, China.
authors.forename: Lixin
authors.initials: L
authors.lastname: Li
authors.forename: Tomoo
authors.initials: T
authors.lastname: Shimada
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Takahashi
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Koumoto
authors.forename: Makoto
authors.initials: M
authors.lastname: Shirakawa
authors.forename: Junpei
authors.initials: J
authors.lastname: Takagi
authors.forename: Xiaonan
authors.initials: X
authors.lastname: Zhao
authors.forename: Baoyu
authors.initials: B
authors.lastname: Tu
authors.forename: Hongmin
authors.initials: H
authors.lastname: Jin
authors.forename: Zhe
authors.initials: Z
authors.lastname: Shen
authors.forename: Baoda
authors.initials: B
authors.lastname: Han
authors.forename: Meihui
authors.initials: M
authors.lastname: Jia
authors.forename: Maki
authors.initials: M
authors.lastname: Kondo
authors.forename: Mikio
authors.initials: M
authors.lastname: Nishimura
authors.forename: Ikuko
authors.initials: I
authors.lastname: Hara-Nishimura
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D054730:Protein Interaction Domains and Motifs; D021381:Protein Transport; D055314:Seed Storage Proteins / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; C518500:Maigo2 protein, Arabidopsis; D055314:Seed Storage Proteins
keywords: Arabidopsis thaliana; MAG2-INTERACTING PROTEIN; SEC1 FAMILY DOMAIN-CONTAINING 2; endoplasmic reticulum; multi-subunit tethering complex; storage proteins