ALG-2 directly binds Sec31A and localizes at endoplasmic reticulum exit sites in a Ca(2+)-dependent manner.
Intracellular localization of the penta-EF-hand Ca(2+)-binding protein ALG-2 in HeLa cells was investigated by immunofluorescent confocal microscopy using a polyclonal antibody. In addition to its presence in the nucleus, ALG-2 was found to be distributed in a punctate pattern in the cytoplasm, where it was partly co-stained with an endoplasmic reticulum (ER) exit site marker p125. In vitro GST pull down analysis demonstrated that ALG-2 and its alternatively spliced isoform interact with the COPII component Sec31A in a Ca(2+)-dependent manner, and a biotin-labeled ALG-2 overlay assay revealed direct binding of ALG-2 to Sec31A. Biochemical and immunofluorescent microscopic analyses showed that ALG-2 was enriched at the Sec31A-localizing membrane compartments upon stimulation with the Ca(2+) ionophore A23187. In contrast, treatment of cells with the membrane-permeant Ca(2+) chelator BAPTA-AM led to a dispersion of ALG-2 throughout the cells and to a significant loss of Sec31A in the perinuclear region. These findings establish Sec31A as a novel target for ALG-2 and provide a framework for studies on the roles of ALG-2 in ER-Golgi transport.[1]References
- ALG-2 directly binds Sec31A and localizes at endoplasmic reticulum exit sites in a Ca(2+)-dependent manner. Shibata, H., Suzuki, H., Yoshida, H., Maki, M. Biochem. Biophys. Res. Commun. (2007) [Pubmed]
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