Research

Analysis of physiological roles of the cytoplasmic PNGase and non-lysosomal catabolic pathway for N-glycans

The Project Leader's Profile

Tadashi Suzuki

Visiting Associate Professor, Osaka University Medical School/ Graduate School of Medicine

Graduated from the Department of Biophysics and Biochemistry, Faculty of Science, University of Tokyo in 1992. Obtained a Ph.D. degree in 1997. From 1997-2000 he was a post-doctoral fellow at the Department of Biochemistry and Cell Biology, State University of New York at Stony Brook. During this period he was a JSPS (Japan Society for the Promotion of Science) pre/postdoctoral fellow for young researchers (1996-1998) and JSPS oversea research fellow (1998-2000). In 2000, he was appointed as a research assistant professor. From December 2001 to March 2005, he served as a researcher of the Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Corporation (JST). From February 2002 he was also an RCF Assistant Professor at the Undergraduate Program for Bioinformatics and Systems Biology (UPBSB), Department of Biophysics and Biochemistry, Graduate School of Science, University of Tokyo. In January 2004, he was appointed as a visiting associate professor at Osaka University Graduate School of Medicine.  From October 2007, he is appointed as a team leader at Glycometabolome Team, RIKEN Advanced Science Institute (ASI).  From April 2008 he is also appointed as a collaborative professor at School of Biomedical Science, Tokyo Medical and Dental University. From April 2010 he is also a visiting professor at Graduate School of Science and Engineering, Saitama University.

Project Leader
  • Tadashi Suzuki, Ph.D., Team Leader, Glycometabolome Team, RIKEN Advanced Science Institute
Research Collaborators

  • Hiroto Hirayama, Ph. D., RIKEN Advanced Science Instiute
  • Akira Hosomi, Ph. D., RIKEN Advanced Science Institute
  • Yoshimi Haga, Ph. D., RIKEN Advanced Science Institute
  • Li Wang, Ph. D., RIKEN Advanced Science Institute
  • Kumiko Ishii, RIKEN Advanced Science Institute
  • Yuki Negishi, RIKEN Advanced Science Institute
  • Junichi Seino, RIKEN Advanced Science Institute
  • Yae Tsuchiya, RIKEN Advanced Science Institute
  • Kotoko Ueno, RIKEN Advanced Science Institute

Summary

Peptide:N-glycanase (PNGase) cleaves asparagine-linked (N-linked) glycan from glycoproteins. Recent studies have shown that this enzyme is involved in quality contol system for newly synthesized glycoproteins in the endoplasmic reticulum (ER). This quality control system distinguishes normal proteins from misfolded and/or unassembled proteins, that are to be degraded by the mechanism called "ER-associated degradation" (ERAD). There is growing evidence that impairment the ERAD function in mammals results in various inherited/acquired neurodegenerative diseases.
We have discovered, purified the cytoplasmic PNGase and subsequently cloned the gene encoding this enzyme. Currently our focus is to analyze structure and function of a newly-found protein complex that involves the cytoplasmic PNGase. It is interesting to note that, while the monocellular organisms such as budding yeast exhibit little effects upon defect of this enzyme, multicellular organisms showed multiple significant phenotypes. We therefore aim to unveil the precise role of PNGase, defect of which causes such pivotal phenotypic consequences. Especially we are interested in how these phenotypes are related to its functional importance in ERAD process.
Occurrence of free N-linked glycan released by PNGase has been known for years. It has been demonstrated in plants that free N-glycans has a hormone-like activity promoting growth and ripening of fruits. Moreover, in mammalian cells extensive biochemical studies revealed the very sophisticated intracellular transport/processing pathway of free N-glycan. However, in either case the molecular mechanism of this process remains largely unknown. For instance, recently the cytoplasmic PNGase was found to play a major role for generating the free N-glycan in the cytosol of budding yeast, while it was also shown that there are still unidentified, PNGase-independent pathway to form free N-glycans.
More recently we have succeeded in cloning the gene encoding the cytoplasmic endo-β-N-acetylglucosaminidase (ENGase) as well as α-mannosidase (Man2C1), which have been believed to be involved in the critical step for the processing of free N-glycans. This finding will lead to the better understanding of processing of free N-glycans, which is still enigmatic even in this "post-genome" era. In the future we'd like to figure out the whole picture of formation, modification and degradation of free N-glycans by identifying molecules involved. The molecular identification of proteins that involved in this process will enable us to assess its functional significance.

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Some of Recent Papers

  1. Hosomi A, Tanabe K, Hirayama H, Kim I, Rao H, and Suzuki T. Identification of Htm1(EDEM)-dependent, Mns1-independent ERAD pathway in Saccharomyces cerevisiae. Application of a novel assay for glycoprotein ERAD. J. Biol. Chem. 285, in press, 2010.
  2. Funakoshi Y, Negishi Y, Gergen JP, Seino J, Ishii K, Lennarz WJ, Matsuo I, Ito Y, Taniguchi N, and Suzuki T. Evidence for an essential deglycosylation-independent activity of PNGase in Drosophila melanogaster. PLoS One 5, e10545, 2010.
  3. Hirayama H, Seino J, Kitajima T, Jigami Y, and Suzuki T. Free oligosaccharides to monitor glycoprotein endoplasmic reticulum-associated degradation in Saccharomyces cerevisiae. J. Biol. Chem. 285, 12390-12404, 2010.
  4. Haga Y, Totani K, Ito Y, and Suzuki T. Establishment of a real-time analytical method for free oligosaccharide transport from the ER to the cytosol. Glycobiology 19, 987-994, 2009
  5. Funakoshi Y, Suzuki T. Glycobiology in the cytosol: the bitter side of a sweet world. Biochim. Biophys. Acta 1790, 81-94, 2009