Membrane localization of a rice calcium-dependent protein kinase (CDPK) ismediated by myristoylation and palmitoylation

Calcium-dependent protein kinases (CDPKs), the most abundant serine/threoni ne kinases in plants, are found in various subcellular localizations, which suggests that this family of kinases may be involved in multiple signal tr ansduction pathways. A complete analysis to try to understand the molecular basis of the presence of CDPKs in various localizations in the cell has no t been accomplished yet. It has been suggested that myristoylation may be r esponsible for membrane association of CDPKs. In this study, we used a rice CDPK, OSCPK2, which has a consensus sequence for myristoylation at the N-t erminus, to address this question. We expressed wild-type OSCPK2 and variou s mutants in different heterologous systems to investigate the factors that affect its membrane association. The results show that OSCPK2 is myristoyl ated and palmitoylated and targeted to the membrane fraction. Both modifica tions are required, myristoylation being essential for membrane localizatio n and palmitoylation for its full association. The fact that palmitoylation is a reversible modification may provide a mechanism for regulation of the subcellular localization. OSCPK2 is the first CDPK shown to be targeted to membranes by an src homology domain 4 (SH4) located at the N-terminus of t he molecule.