title: The regulation of ER export and Golgi retention of ST3Gal5 (GM3/GM4 synthase) and B4GalNAcT1 (GM2/GD2/GA2 synthase) by arginine/lysine-based motif adjacent to the transmembrane domain.
abstract: In the Golgi maturation model, the Golgi cisternae dynamically mature along a secretory pathway. In this dynamic process, glycosyltransferases are transported from the endoplasmic reticulum (ER) to the Golgi apparatus where they remain and function. The precise mechanism behind this maturation process remains unclear. We investigated two glycosyltransferases, ST3Gal5 (ST3G5) and B4GalNAcT1 (B4GN1), involved in ganglioside synthesis and examined their signal sequences for ER export and Golgi retention. Reports have suggested that the [R/K](X)[R/K] motif functions as an ER exporting signal; however, this signal sequence is insufficient in stably expressed, full-length ST3G5. Through further analysis, we have clarified that the (2)R(3)R(X)(5) (9)K(X)(3) (13)K sequence in ST3G5 is essential for ER export. We have named the sequence the R/K-based motif. On the other hand, for ER export of B4GN1, the homodimer formation in addition to the R/K-based motif is required for ER export suggesting the importance of unidentified lumenal side interaction. We found that ST3G5 R2A/R3A and K9A/K13A mutants localized not only in Golgi apparatus but also in endosomes. Furthermore, the amounts of mature type asparagine-linked (N)-glycans in ST3G5 R2A/R3A and K9A/K13A mutants were decreased compared with those in wild-type proteins, and the stability of the mutants was lower. These results suggest that the R/K-based motif is necessary for the Golgi retention of ST3G5 and that the retention is involved in the maturation of N-glycans and in stability. Thus, several basic amino acids located on the cytoplasmic tail of ST3G5 play important roles in both ER export and Golgi retention.
authors.affiliation: Division of Glycopathology, Institute of Molecular Biomembrane and Glycobiology, Tohoku Pharmaceutical University, 4-4-1, Komatsushima, Aoba-ku, Sendai, Miyagi 981-8558, Japan The Molecular Genetic Research, Department of Chemistry and Biological Science, College of Science and Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuo-ku, Sagamihara 252-5258, Japan jin@tohoku-pharm.ac.jp uemura@chem.aoyama.ac.jp.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Uemura
authors.affiliation: Division of Glycopathology, Institute of Molecular Biomembrane and Glycobiology, Tohoku Pharmaceutical University, 4-4-1, Komatsushima, Aoba-ku, Sendai, Miyagi 981-8558, Japan.
authors.forename: Fumi
authors.initials: F
authors.lastname: Shishido
authors.affiliation: Division of Glycopathology, Institute of Molecular Biomembrane and Glycobiology, Tohoku Pharmaceutical University, 4-4-1, Komatsushima, Aoba-ku, Sendai, Miyagi 981-8558, Japan.
authors.forename: Madoka
authors.initials: M
authors.lastname: Kashimura
authors.affiliation: Division of Glycopathology, Institute of Molecular Biomembrane and Glycobiology, Tohoku Pharmaceutical University, 4-4-1, Komatsushima, Aoba-ku, Sendai, Miyagi 981-8558, Japan jin@tohoku-pharm.ac.jp uemura@chem.aoyama.ac.jp.
authors.forename: Jin-ichi
authors.initials: J
authors.lastname: Inokuchi
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D001120:Arginine / Q000235:genetics; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D008239:Lysine / Q000235:genetics; D051379:Mice; D009154:Mutation; D017350:N-Acetylgalactosaminyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012799:Sialyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D021382:Protein Sorting Signals; D001120:Arginine; D017350:N-Acetylgalactosaminyltransferases; C023220:(N-acetylneuraminyl)-galactosylglucosylceramide N-acetylgalactosaminyltransferase; D012799:Sialyltransferases; C021343:haematoside synthetase; D008239:Lysine
keywords: ER export; Golgi retention; glycosphingolipid; glycosyltransferase