| Research Abstract |
HPC-1/syntaxin lA (HPC-l), which plays an important role in vesicular transport to the plasma membrane, possesses a hydrophobic sequence at its C terminus, In the present study, we investigated the role of the C-terminal portion of HPC-1 in intracellular localization. When expressed from cDNA in COS cells, wild-type HPC-1 was localized in the Golgi complex and the plasma membrane. HPC-l localized in the Golgi complex was chased away to the plasma membrane in the presence of cycloheximide. Truncation of the hydrophobic domain resulted in the cytoplasmic localization of the mutant, thus indicating that the domain indeed functions as a membrane anchor. The fusion protein with the N-terminal region of bovine opsin (the 0P3 extension), which contains the N-glycosylation sites, was glycosylated in transfected COS cells. In addition, we found that a chimeric protein consisting of Escherichia coil maltose binding protein with the last 24 amino acids of HPC-1 and the 0P3 extension is also glycosylated and localized along the exocytic pathway of transfected cells similar to HPC- 1. Taken together, these indicate that HPC-1 has a transmembrane structure, and suggest that the protein is first inserted into the endoplasmic reticulum and then transported to the plasma membrane via the exocytic pathway. In addition, our results indicate that the C-terminal portion of HPC-1is important for its intracellular localization.
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