GnT1IP-L specifically inhibits MGAT1 in the Golgi via its luminal domain

• Main Authors: Hung-Hsiang Huang, Antti Hassinen, Subha Sundaram, Andrej-Nikolai Spiess, Sakari Kellokumpu, Pamela Stanley
• Format: Article
• Language: English
• Published: eLife Sciences Publications Ltd 2015-09-01
• Series: eLife
• Subjects: GnT1IP-L; MGAT1 inhibitor; complex N-glycans; Golgi interaction; spermatogenesis
• Online Access: https://elifesciences.org/articles/08916

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.