| Research Abstract |
Newly synthesized proteins in the ER(endoplasmic reticulum) are sorted out to the secretory pathway after they fold or assemble correctly, while misfoled or misassembled proteins are retained in the ER. This mechanism is known as ER quality control. Misfolded proteins in the ER are retrotranslocated out of the ER,followed by degradation by cytosolic proteasome, which is called as ERAD(ER associated degradation). We have cloned a mouse gene, and named it as EDEM(ER degradation enhancing α-mannosidase like-protein), which accelerated the ERAD of misfolded glycoproteins.
In the present study, we have clarified the followings:
1. We are usingα1-antitrypsin variant null (Hong Kong) (NHK)as a model substrate for ERAD. It is known that the mannose trimming by the ER Mannosidase I(ER Man I) become the signal for glycoprotein ERAD. We have clarified that overexpression of ER Man I into human embryonic kidney 293 cells enhanced the degration of NHK. We also found that the effect of ER Man I and EDEM are additive. We conclude that the misfolded glycoproteins are recognized both by ER Man I and by EDEM before they are degraded
2. NHK has one cysteine residue near its Cterminus, thus it is possible that they make disulfide-bonded dimer. We have clarified that NHK make homodimer within the cells, and that coexpression of EDEM inhibited the dimer formation. Disulfide-bonded dimer is expectedly retrotraslocated out of the ER less effciently. On the contrary, EDEM did not affect the secretion or degradation of wild type α1-antitrypsin, which folds correctly in the ER. Taken together, we expect that EDEM keep the misfolded glycoprotein degradation competent
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