| Budget Amount *help |
¥2,800,000 (Direct Cost: ¥2,800,000)
Fiscal Year 2004: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2003: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
In the present study, I have further analyzed the function of EDEM (ER degradation enhancing α-mannosidase-like protein), which accelerates ERAD (ER associated degradation) of glycoproteins (EMBO Reports, 2,415-422 (2001)). The results which I obtained are summarized as follows :
1.ER mannosidase I(ER ManI) is an enzyme which trimmes mannose residues from N-linked oligosaccharides, and this trimming is a key event that triggers a misfolded glycoprotein for ERAD. EDEM is homologous to ER ManI, but we have found that EDEM lacks enzyme activity as a processing α-mannosidase. By analyzing the oligosaccharide structures on misfolded NHK(α1-antitrypsin variant null Hong Kong), we have clarified that the mechanisms of ER ManI and EDEM on glycoprotein ERAd are different (JBC, 278, 26287-26294, (2003)).
2.An ERAD substrate NHK has one cysteine residue near its C-terminus, and we have found that NHK makes an intramolecular disulfide bridge, resulting in NHK dimer formation within the cells. EDEM overexpression inhibited NHK dimer formation, whereas EDEM had no effect on the synthesis and secretion of wild type α1-antitrypsin. These results suggested that EDEM binds to misfolded glycoproteins in the ER, and that it acts like a molecular chaperone protein of misfolded glycoproteins by keeping them degradation competent.
3.We have cloned an EDEM homologue protein, which we named EDEM3. EDEM3 is an ER lumemal protein, and enhanced the glycoprotein ERAD like EDEM1 when it was overexpressed in 293 cells. We have found that the mechanisms of these homologue proteins on glycoprotein ERAD are discrete and that their expressions are differently regulated by the ER stress and in tissues.
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