Important roles of the C-terminal portion of HPC-1/syntaxin 1A in membrane anchoring and intracellular localization

HPC-1/syntaxin 1A (HPC-1), which plays an important role in vesicular transport to the plasma membrane, possesses a hydrophobic sequence at its C terminus. When expressed from cDNA in COS cells, wild-type HPC-1 was localized in the Golgi complex and the plasma membrane. Truncation of the hydrophobic domain resulted in the cytoplasmic localization of the mutant, thus indicating that the domain indeed functions as a membrane anchor. A fusion protein with the C-terminal glycosylation sites was glycosylated in transfected cells, providing evidence that HPC-1 has a transmembrane structure, and that the protein is first inserted into the endoplasmic reticulum and then transported to the plasma membrane. A chimeric protein consisting of Escherichia coli maltose-binding protein with the last 24 amino acids of HPC-1 was inserted into the endoplasmic reticulum in a transmembrane topology and localized along the exocytic pathway of transfected cells similar to HPC-1, These results indicate that the portion is important for intracellular localization of HPC-1.