title: GnT1IP-L specifically inhibits MGAT1 in the Golgi via its luminal domain.
abstract: Mouse GnT1IP-L, and membrane-bound GnT1IP-S (MGAT4D) expressed in cultured cells inhibit MGAT1, the N-acetylglucosaminyltransferase that initiates the synthesis of hybrid and complex N-glycans. However, it is not known where in the secretory pathway GnT1IP-L inhibits MGAT1, nor whether GnT1IP-L inhibits other N-glycan branching N-acetylglucosaminyltransferases of the medial Golgi. We show here that the luminal domain of GnT1IP-L contains its inhibitory activity. Retention of GnT1IP-L in the endoplasmic reticulum (ER) via the N-terminal region of human invariant chain p33, with or without C-terminal KDEL, markedly reduced inhibitory activity. Dynamic fluorescent resonance energy transfer (FRET) and bimolecular fluorescence complementation (BiFC) assays revealed homomeric interactions for GnT1IP-L in the ER, and heteromeric interactions with MGAT1 in the Golgi. GnT1IP-L did not generate a FRET signal with MGAT2, MGAT3, MGAT4B or MGAT5 medial Golgi GlcNAc-tranferases. GnT1IP/Mgat4d transcripts are expressed predominantly in spermatocytes and spermatids in mouse, and are reduced in men with impaired spermatogenesis.
authors.affiliation: Department of Cell Biology, Albert Einstein College of Medicine, New York, United States.
authors.forename: Hung-Hsiang
authors.initials: HH
authors.lastname: Huang
authors.affiliation: Faculty of Biochemistry and Molecular Medicine, University of Oulu, Oulu, Finland.
authors.forename: Antti
authors.initials: A
authors.lastname: Hassinen
authors.affiliation: Department of Cell Biology, Albert Einstein College of Medicine, New York, United States.
authors.forename: Subha
authors.initials: S
authors.lastname: Sundaram
authors.affiliation: Andrology Division, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Andrej-Nikolai
authors.initials: AN
authors.lastname: Spiess
authors.affiliation: Faculty of Biochemistry and Molecular Medicine, University of Oulu, Oulu, Finland.
authors.forename: Sakari
authors.initials: S
authors.lastname: Kellokumpu
authors.affiliation: Department of Cell Biology, Albert Einstein College of Medicine, New York, United States.
authors.forename: Pamela
authors.initials: P
authors.lastname: Stanley
mesh_terms: D000818:Animals; D031541:Fluorescence Resonance Energy Transfer; D006056:Golgi Apparatus / Q000378:metabolism*; D006801:Humans; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D017351:N-Acetylglucosaminyltransferases / Q000037:antagonists & inhibitors*; D011485:Protein Binding; D025941:Protein Interaction Mapping
chemical_list: C000608129:MGAT4D protein, human; D008565:Membrane Proteins; C561128:MGAT1 protein, human; D017351:N-Acetylglucosaminyltransferases
keywords: GnT1IP-L; Golgi interactions; MGAT1 inhibitor; cell biology; complex N-glycans; human; mouse; spermatogenesis