2007 Fiscal Year Final Research Report Summary
Mechanisms and Physiological Roles of Endoplacmic Reticulum Quality Control Regulated by Protein Glycosylation
| Project/Area Number |
17370067
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Cell biology
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| Research Institution | Nagoya University |
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Principal Investigator |
NISHIKAWA Shuh-ichi Nagoya University, Graduate School of Science, Associate Professor (10252222)
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| Co-Investigator(Kenkyū-buntansha) |
ENDO Toshiya Nagoya University, Graduate School of Science, Professor (70152014)
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| Project Period (FY) |
2005 – 2007
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| Keywords | Endoplasmic Reticulum / Quality Control / Protein Glycosylation / Molecular Chaperone |
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| Research Abstract |
The endoplasmic reticulum (ER) is the entrance of the secretory pathway in eukaryotic cells. Secretory and membrane proteins undergo folding and various modification processes before they are exported to the Golgi apparatus. Quality control mechanisms in the ER monitor these processes to ensure that defective proteins that failed to acquire correct functional structures are not deployed throughout the cells. Misfolded proteins retained in the ER are degraded by a mechanism called endoplasmic reticulum-associated degradation (ERAD) . The aim of our research is to elucidate mechanisms of the ER quality control system mediated by carbohydrate modification of proteins using budding yeast and Arabidopsis thaliana.
Yeast Mnllp is a mannosidase family protein in the ER and is proposed to function in the substrate recognition in the ERAD of misfolded glycoproteins. We found that Mnllp forms a complex with protein disulfide isomerase (PDI) through disulfide bonds. Analyses using mutants of Mnllp
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and PDI showed that the Mnll p-PDI interaction is important for ERAD. To analyze relationships between protein folding and carbohydrate modification in substrate recognition in ERAD, we developed new ERAD substrates using CPY*, a widely used ERAD substrate in yeast. Analyses using the newly developed ERAD substrates showed that a N-linked carbohydrate chain required for ERAD of CPY* is recognized as a ERAD signal only when it was in the misfolded domain.
Analyses using mammalian and yeast cells showed that calnexin/calreticulin, EDEM (Mnllp in yeast) and OS9 function in carbohydrate chain-mediated ER quality control. Arabidopsis has orthologs of these ER quality control machineries. We constructed Arabidopsis knockout mutants of these quality control machineries and found that simultaneous deletion of AtCNX1 and AtCRT1 resulted in growth retardation. We also constructed AtCPY*-GFP, a novel ERAD substrate in plant cells. In contrast to yeast CPY*, we showed that ERAD of AtCPY*GFP does not require its N-linked carbohydrate modification Less
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