| Summary: | 碩士 === 國立臺灣大學 === 生化科學研究所 === 90 === The human endogenous retrovirus (HERV) sequence occupies about 1% of the human genome. Transcripts of HERVs including gag, pol, or env can be expressed in many tissues, but most of them are incomplete due to accumulated mutations in viral genomes during evolution.
HERV-W is one of recently identified HERVs. The envelope (env) gene of HERV-W encodes a functional protein called syncytin, which is specifically expressed in syncytiotrophblasts. Syncytin has been shown to mediate fusion of human cytotrophoblast cells into syncytiotrophoblast. However, it is still not clear how this membrane gylcoprotein mediate cell-cell fusion. The syncytin gene is predicted to encode a polypeptide of 538 amino acids. After synthesis, a post-translational cleavage is occurred and separated syncytin polypeptide into surface subunit (SU) and transmembrane subunit (TM).
To functionally characterize syncytin, we constructed 40 syncytin mutants including the mutants derived from linker scanning mutagenesis, point mutation at the glycosylation site, and deletion of cytoplasmic domain (CTD). Our results indicated that most mutant constructs in SU subunit of syncytin lost their fusogenic activities and the glycosylation site of the TM domain is not critical. In contrast, the CTD mutant enhanced the fusogenic activity. Our results suggested that the CTD of syncytin may affect syncytin-mediated fusion by either intra- or intermolecular interaction with itself or unknown factors.
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