title: Distinct transport and intracellular activities of two GlcAT-P isoforms.
abstract: A neural glycotope, human natural killer-1 carbohydrate, is involved in synaptic plasticity. The key biosynthetic enzyme is a glucuronyltransferase, GlcAT-P, a type II membrane protein comprising an N-terminal cytoplasmic tail, transmembrane domain, stem region, and C-terminal catalytic domain. Previously, we reported that GlcAT-P has two isoforms differing in only the presence or absence of the N-terminal 13 amino acids (P-N13) in the cytoplasmic tail, but the functional distinction of these two isoforms has not been reported. Herein, we show that when expressed in Neuro2A cells, short form GlcAT-P (sGlcAT-P) exhibited significantly higher glucuronylation activity than the longer form (lGlcAT-P), despite their comparable specific activities in vitro. In addition, sGlcAT-P was strictly localized in Golgi apparatus, whereas lGlcAT-P was mainly localized in Golgi but partly in the endoplasmic reticulum. We demonstrated that the small GTPase, Sar1, recognized a dibasic motif in the cytoplasmic tail near P-N13 that was important for exiting the endoplasmic reticulum, and Sar1 interacted with sGlcAT-P more strongly than lGlcAT-P. Finally, the attachment of P-N13 to another glycosyltransferase, polysialyltransferase-I (ST8Sia-IV), had similar effects, such as reduced activity and entrapment within endoplasmic reticulum. These results suggest that P-N13 can control glycosyltransferase transport through Sar1 binding interference.
authors.affiliation: Department of Biological Chemistry, Graduate School of Pharmaceutical Sciences, Kyoto University, Kyoto 606-8507, Japan.
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Kizuka
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Tonoyama
authors.forename: Shogo
authors.initials: S
authors.lastname: Oka
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D014453:Glucuronosyltransferase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D042541:Intracellular Space / Q000201:enzymology*; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D021381:Protein Transport; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D011994:Recombinant Proteins; C111364:galactosylgalactoylxylosylprotein 3-beta-glucuronosyltransferase; D014453:Glucuronosyltransferase; D020559:Monomeric GTP-Binding Proteins