1 research outputs found
Identification and characterization of the COPII vesicleāforming GTPase Sar1 in Chlamydomonas
Abstract Eukaryotic cells are highly compartmentalized, requiring elaborate transport mechanisms to facilitate the movement of proteins between membraneābound compartments. Most proteins synthesized in the endoplasmic reticulum (ER) are transported to the Golgi apparatus through COPIIāmediated vesicular trafficking. Sar1, a small GTPase that facilitates the formation of COPII vesicles, plays a critical role in the early steps of this protein secretory pathway. Sar1 was characterized in yeast, animals and plants, but no Sar1 homolog has been identified and functionally analyzed in algae. Here we identified a putative Sar1 homolog (CrSar1) in the model green alga Chlamydomonas reinhardtii through amino acid sequence similarity. We employed siteādirected mutagenesis to generate a dominantānegative mutant of CrSar1 (CrSar1DN). Using protein secretion assays, we demonstrate the inhibitory effect of CrSar1DN on protein secretion. However, different from previously studied organisms, ectopic expression of CrSar1DN did not result in collapse of the ERāGolgi interface in Chlamydomonas. Nonetheless, our data suggest a largely conserved role of CrSar1 in the ERātoāGolgi protein secretory pathway in green algae