Abstract
Regulation by Ca2+ of protein dephosphorylation in plants is not well understood, since calmodulin-dependent protein phosphatase (PP2B) conserved in both animals and yeasts has not been characterized in plants. Screening of the cDNA library of the moss Physcomitrella patens by using 35S-labeled calmodulin identified PCaMPP gene encoding a protein similar to protein phosphatase 2C. Bacterially expressed recombinant GST-PCaMPP bound calmodulin-Sepharose. The protein exhibited phosphatase activity to phosphorylated myelin basic protein and the activity was dramatically increased by Mn2+. Furthermore, the activity was insensitive to okadaic acid. PCaMPP lost both calmodulin-binding ability and phosphatase activity by deletion of the C-terminal region containing basic amphiphilic amino acid sequence. A synthetic peptide with this sequence bound calmodulin in a Ca2+-dependent manner. A gene similar to PCaMPP was found in Arabidopsis genome suggesting that it is a protein phosphatase conserved in land plants.
