title: Free oligosaccharides in the cytosol of Caenorhabditis elegans are generated through endoplasmic reticulum-golgi trafficking.
abstract: Free oligosaccharides (FOSs) in the cytosol of eukaryotic cells are mainly generated during endoplasmic reticulum (ER)-associated degradation (ERAD) of misfolded glycoproteins. We analyzed FOS of the nematode Caenorhabditis elegans to elucidate its detailed degradation pathway. The major FOSs were high mannose-type ones bearing 3-9 Man residues. About 94% of the total FOSs had one GlcNAc at their reducing end (FOS-GN1), and the remaining 6% had two GlcNAc (FOS-GN2). A cytosolic endo-beta-N-acetylglucosaminidase mutant (tm1208) accumulated FOS-GN2, indicating involvement of the enzyme in conversion of FOS-GN2 into FOS-GN1. The most abundant FOS in the wild type was Man(5)GlcNAc(1), the M5A' isomer (Manalpha1-3(Manalpha1-6)Manalpha1-6(Manalpha1-3)Manbeta1-4GlcNAc), which is different from the corresponding M5B' (Manalpha1-2Manalpha1-2Manalpha1-3(Manalpha1-6)Manbeta1-4GlcNAc) in mammals. Analyses of FOS in worms treated with Golgi alpha-mannosidase I inhibitors revealed decreases in Man(5)GlcNAc(1) and increases in Man(7)GlcNAc(1). These results suggested that Golgi alpha-mannosidase I-like enzyme is involved in the production of Man(5-6)-GlcNAc(1), which is unlike in mammals, in which cytosolic alpha-mannosidase is involved. Thus, we assumed that major FOSs in C. elegans were generated through Golgi trafficking. Analysis of FOSs from a Golgi alpha-mannosidase II mutant (tm1078) supported this idea, because GlcNAc(1)Man(5)GlcNAc(1), which is formed by the Golgi-resident GlcNAc-transferase I, was found as a FOS in the mutant. We concluded that significant amounts of misfolded glycoproteins in C. elegans are trafficked to the Golgi and are directly or indirectly retro-translocated into the cytosol to be degraded.
authors.affiliation: Division of Integrated Life Science, Graduate School of Biostudies, Kyoto University, Kitashirakawa, Kyoto, Japan.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Kato
authors.forename: Kumiko
authors.initials: K
authors.lastname: Kitamura
authors.forename: Megumi
authors.initials: M
authors.lastname: Maeda
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Kimura
authors.forename: Takane
authors.initials: T
authors.lastname: Katayama
authors.forename: Hisashi
authors.initials: H
authors.lastname: Ashida
authors.forename: Kenji
authors.initials: K
authors.lastname: Yamamoto
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000502:physiology*; D003600:Cytosol / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000502:physiology*; D006056:Golgi Apparatus / Q000502:physiology*; D009844:Oligosaccharides / Q000302:isolation & purification / Q000378:metabolism*; D017026:Swainsonine / Q000494:pharmacology
chemical_list: D009844:Oligosaccharides; D017026:Swainsonine