2. Academic Validation
  3. Identification of a Golgi GPI-N-acetylgalactosamine transferase with tandem transmembrane regions in the catalytic domain

Identification of a Golgi GPI-N-acetylgalactosamine transferase with tandem transmembrane regions in the catalytic domain

  • Nat Commun. 2018 Jan 26;9(1):405. doi: 10.1038/s41467-017-02799-0.
Tetsuya Hirata 1 2 3,  Sushil K Mishra 4,  Shota Nakamura 1,  Kazunobu Saito 1,  Daisuke Motooka 1,  Yoko Takada 2,  Noriyuki Kanzawa 1 2,  Yoshiko Murakami 1 2,  Yusuke Maeda 1 2,  Morihisa Fujita 5,  Yoshiki Yamaguchi 4,  Taroh Kinoshita 6 7
Affiliations

Affiliations

  • 1 Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, 565-0871, Japan.
  • 2 WPI Immunology Frontier Research Center, Osaka University, Suita, Osaka, 565-0871, Japan.
  • 3 National Institute for Physiological Sciences, National Institutes of Natural Sciences, Okazaki, Aichi, 444-8787, Japan.
  • 4 Structural Glycobiology Team, Systems Glycobiology Research Group, RIKEN Global Research Cluster, Wako, Saitama, 351-0198, Japan.
  • 5 Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, Jiangsu, 214122, China.
  • 6 Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, 565-0871, Japan. [email protected].
  • 7 WPI Immunology Frontier Research Center, Osaka University, Suita, Osaka, 565-0871, Japan. [email protected].
PMID: 29374258 DOI: 10.1038/s41467-017-02799-0
Abstract

Many eukaryotic proteins are anchored to the cell surface via the glycolipid glycosylphosphatidylinositol (GPI). Mammalian GPIs have a conserved core but exhibit diverse N-acetylgalactosamine (GalNAc) modifications, which are added via a yet unresolved process. Here we identify the Golgi-resident GPI-GalNAc transferase PGAP4 and show by mass spectrometry that PGAP4 knockout cells lose GPI-GalNAc structures. Furthermore, we demonstrate that PGAP4, in contrast to known Golgi glycosyltransferases, is not a single-pass membrane protein but contains three transmembrane domains, including a tandem transmembrane domain insertion into its glycosyltransferase-A fold as indicated by comparative modeling. Mutational analysis reveals a catalytic site, a DXD-like motif for UDP-GalNAc donor binding, and several residues potentially involved in acceptor binding. We suggest that a juxtamembrane region of PGAP4 accommodates various GPI-anchored proteins, presenting their acceptor residue toward the catalytic center. In summary, we present insights into the structure of PGAP4 and elucidate the initial step of GPI-GalNAc biosynthesis.

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