Phosphorylation Properties of Recombinant OsCPK11, a Calcium-dependent Protein Kinase from Rice

Abstract

In plants, calcium (Ca2+)-dependent protein kinases (CDPKs) are important sensors of Ca2+ signals. Previous research demonstrated the expression of the OsCPK11 gene in various tissues at the transcription level, but its developmental and biochemical functions at the protein level were not determined. This study was aimed to identify biochemical characteristics of OsCPK11. GST- OsCPK11 was expressed in E. coli and used for an in vitro kinase assay. Biochemical analyses identified OsCPK11 as a CDPK. OsCPK11 autophosphorylated itself and transphosphorylated histone III-s and MBP as substrates in the presence of Ca2+. The activity of the recombinant OsCPK11 was influenced by Mg2+, with optimum activity detected at pH 7.0-7.5. OsCPK11 activity was not affected by Mg2+, Mn2+, or Na+ in the presence of a high level of Ca2+. Autophosphorylation of OsCPK11 decreased Ca2+ sensitivity of OsCPK11. An anti-OsCPK11 rabbit antibody recognized 95.5 kD of GST-OsCPK11, as shown by an immunoblot analysis. These results shed light on the function of OsCPK11 in Ca2+-mediated signaling in rice.