NHE6 protein possesses a signal peptide destined for endoplasmic reticulum membrane and localizes in secretory organelles of the cell

被引:76
作者
Miyazaki, E
Sakaguchi, M
Wakabayashi, S
Shigekawa, M
Mihara, K
机构
[1] Kyushu Univ, Grad Sch Med Sci, Dept Mol Biol, Higashi Ku, Fukuoka 8128582, Japan
[2] Natl Cardiovasc Ctr, Res Inst, Dept Mol Physiol, Suita, Osaka 5658565, Japan
关键词
D O I
10.1074/jbc.M106267200
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The NHE6 protein is a unique Na+/H+ exchanger isoform believed to localize in mitochondria. It possesses a hydrophilic N-terminal portion that is rich in positively charged residues and many hydrophobic segments. In the present study, signal sequences in the NHE6 molecule were examined for organelle localization and membrane topogenesis. When the full-length protein was expressed in COS7 cells, it localized in the endoplasmic reticulum and on the cell surface. Furthermore, the protein was fully N-glycosylated, When green fluorescent protein was fused after the second (H2) or third (H3) hydrophobic segment, the fusion proteins were targeted to the endoplasmic reticulum (ER) membrane. The localization pattern was the same as that of fusion proteins in which green fluorescent protein was fused after H2 of NHE1 In an in vitro system, H1 behaved as a signal peptide that directs the translocation of the following polypeptide chain and is then processed off. The next hydrophobic segment (H2) halted translocation and eventually became a transmembrane segment. The N-terminal hydrophobic segment (H1) of NHE1 also behaved as a signal peptide. Cell fractionation studies using antibodies against the 15 C-terminal residues indicated that NHE6 protein localized in the microsomal membranes of rat liver cells. All of the NHE6 molecules in liver tissue possess an endoglycosidase H-resistant sugar chain. These findings indicate that NHE6 protein is targeted to the ER membrane via the N-terminal signal peptide and is sorted to organelle membranes derived from the ER membrane.
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页码:49221 / 49227
页数:7
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