Functional characterization of the placental fusogenic membrane protein syncytin
Functional characterization of the placental fusogenic membrane protein syncytin
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DOI：
10.1095/biolreprod.104.033340
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发表时间：
2004-12-01
影响因子：
3.6
通讯作者：
Chen, H
中科院分区：
文献类型：
--
作者：
Chang, C;Chen, PT;Chen, H
合胞素是人类内源性逆转录病毒W家族(Herv-W)的囊膜蛋白。合胞素在人胎盘中特异表达，并介导滋养层细胞融合成多核合体滋养层。它是一个由538个氨基酸组成的多肽，被预测在翻译后被切割成表面(SU)亚基和跨膜(TM)亚基。研究合胞素蛋白的功能有助于理解合胞素介导的细胞融合的分子机制。在这篇报道中，我们研究了合胞素在293T和HeLa细胞中的结构与功能的关系，这些细胞瞬时表达了野生型合胞素或通过接头扫描和缺失突变产生的合胞素突变体。在插入接头的22个突变体中，Ins(51)、Inv(139)、ine(156)、Ins(493)、Ina(506)和Inl(529)是融合型的，这表明SU亚基的氨基酸S-51、V-139和E-116以及S-493、A(506)附近的区域是融合的。而位于合胞素胞质结构域的L-529则构象灵活。在17个缺失突变体中，有9个氨基酸479~538缺失的突变体是融合子。缺失突变体DELL(480)与野生型相比，只含有胞质区域的前四个氨基酸残基，具有更强的融合活性。此外，在合胞素的TM亚基中还定义了两个七肽重复区域(HRA和113)。一种源自C-末端七重复区(HRB)的多肽抑制物被证明能有效地抑制合胞素介导的细胞融合。我们的结果表明，合胞素的胞质结构域对合胞素介导的融合不是必需的，但可能起到调节作用，并且HRA和B之间的分子内相互作用参与了融合过程。
Syncytin is an envelope protein of the human endogenous retrovirus family W (HERV-W). Syncytin is specifically expressed in the human placenta and mediates trophoblast cell fusion into the multinucleated syncytiotrophoblast layer. It is a polypeptide of 538 amino acids and is predicted to be posttranslationally cleaved into a surface (SU) subunit and a transmembrane (TM) subunit. Functional characterization of syncytin protein can aid understanding of the molecular mechanism underlying syncytin-mediated cell fusion. In this report, we studied the structure-function relationship of syncytin in 293T and HeLa cells transiently expressing wild-type syncytin or syncytin mutants generated by linker scanning and deletion mutagenesis. Of the 22 linker-inserted mutants, mutants InS(51), InV(139), InE(156), InS(493), InA(506), and InL(529) were fusogenic, suggesting that regions around amino acids S-51, V-139, and E-116 in the SU subunit and S-493, A(506). and L-529 in the cytoplasmic domain (CTM) of syncytin are flexible in conformation. Of the 17 deletion mutants, nine mutants with deletions in the region from amino acids 479 to 538 were fusogenic. The deletion mutant Dell(480), containing only the first four amino acid residues in the cytoplasmic domain, had enhanced fusogenic activity in comparison with the wild-type. In addition, two heptad repeat regions (HRA and 113) were defined in the TM subunit of syncytin. A peptide inhibitor derived from the C-terminal heptad repeat region (HRB) was shown to potently inhibit syncytin-mediated cell fusion. Our results suggest that the cytoplasmic domain of syncytin is not essential for syncytin-mediated fusion but may play a regulatory role, and an intramolecular interaction between HRA and B is involved in the fusion process.