Abstract
Alexandrium pacificum is a typical dinoflagellate that can cause harmful algal blooms, resulting in negative impacts on ecology and human health. The calcium (Ca(2+)) signal transduction pathway plays an important role in cell proliferation. Calmodulin (CaM) and CaM-related proteins are the main cellular Ca(2+) sensors, and can act as an intermediate in the Ca(2+) signal transduction pathway. In this study, the proteins that interacted with CaM of A. pacificum were screened by two-dimensional electrophoresis analysis and far western blots under different growth conditions including lag phase and high phosphorus and manganese induced log phase (HPM). The interactive proteins were then identified using matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Four proteins were identified, including Ca(2+)/CaM-dependent protein kinase, serine/threonine kinase, annexin, and inositol-3-phosphate synthase, which all showed high expression levels under HPM. The gene expression levels encoding these four proteins were also up-regulated under HPM, as revealed by quantitative polymerase chain reaction, suggesting that the identified proteins participate in the Ca(2+) transport channel and cell cycle regulation to promote cell division. A network of proteins interacting with CaM and their target proteins involved in the regulation of cell proliferation was raised, which provided new insights into the mechanisms behind the explosive growth of A. pacificum.