AC29: the most abundant protein of Alexandrium catenella and its potential use in encystment/excystment studies

The objective of this research was to characterize specific protein(s) from Alexandrium catenella to evaluate its use as markers for specific physiological functions. To identify such protein(s) we concentrated our efforts on characterizing proteins with a high level of expression in vegetative cells of A. catenella. The electrophoretic analysis of a total protein cell extract showed the presence of a very abundant 29 kDa protein that we have named AC29. Analysis by 2D SDS-PAGE shows that the 29 kDa band contains one abundant protein (AC29) and various less abundant polypeptides, suggesting the presence of either different proteins with similar molecular weight or isoforms of AC29 protein. Ultracytolocalization using antibodies raised against gel purified AC29 indicates that this protein localizes within the chloroplast and that it is associated with thylakoid membranes, as well as with other membranes surrounding the chloroplast. Western blot analysis of cells grown under light starvation shows that the expression of the AC29 protein is down regulated. A similar analysis shows that this protein is not expressed in natural cysts or by isolated intracellular bacterium. The amino terminus of the AC29 protein that was recovered from 2D SDS-PAGE was sequenced. The sequence shows homology to the peridinin-chlorophyll a-protein from the marine organisms Alexandrium cohorticula, Amphidinium carterae and Symbiodinium. Based on these results, we suggest that the AC29 protein has the potential of being used as a marker for A. catenella encystment and excystment processes.