Isolation of plasma-membrane-bound calcium/calmodulin-regulated protein kinase from pea using Western blotting

Organ-specific and light-induced expression of plant genes

Light plays a pivotal role in the development of plants. The photoregulation of plant genes involves recognition of light quality and quantity by phytochrome and other light receptors. Two gene families, rbcS and Cab, which code for abundant proteins active in photosynthesis, the small subunit of ribulose bisphosphate carboxylase and the chlorophyll a/b binding protein, show a 20-to 50-fold increase in transcript abundance in the light. Analyses in calli and transgenic plants of deletions of the rbcS gene and of chimeric constructions has allowed localization of two regions involved in light-induced transcription. One element is confined to a 33-base pair region surrounding the TATA box. In addition, an enhancer-like element contained within a 240-base pair fragment can confer phytochrome-induced transcription and organ specificity on nonregulated promoters.

Endogenous protein phosphorylation and protein kinase activity in winged bean

In winged bean (Psophocarpus tetragonolobus) protein kinases (E.C. 2.7.1.37) were found in all tissues studied. There was a significant increase in kinase activity during seed development, with a concomitant enhancement in the phosphorylation of a number of polypeptides; this was reversed in germinating seed cotyledons. Protein phosphorylation was apparently correlated with the increase in the protein content of the developing seed and the growing axis. At least three distinct autophosphorylating proteins could be distinguished in the developing seeds after SDS-PAGE, indicating the presence of different types of protein kinases in winged bean.

Calcium-dependent protein kinase from apple fruit membranes is calmodulin-independent but has calmodulin-like properties

Crude Ca(2+)-activated protein kinase from membranes of apple (Malus domestica L. Borkh., Cox's Orange Pippin) fruit can be partially purified to yield a Ca(2+)-dependent protein kinase whose activity is apparently not regulated by calmodulin. The autophosphorylating catalytic subunit of this protein kinase shows a Ca(2+)-dependent mobility shift of approx. 10 kilodaltons (kDa) on sodium dodecyl sulphate-polyacrylamide gel electrophoresis; in the absence of added Ca(2+) or ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) its apparent molecular mass is approx. 50 kDa. The Ca(2+)-dependent protein kinase is inhibited by the calmodulin antagonists N-(6-aminohexyl)-5-chloro-1-naphthalenesulphonamide and trifluoperazine with IC50 values of approx. 45 μM and 15 μM, respectively. These similarities between the protein kinase and calmodulin indicate that the kinase may be a calmodulin-like protein.

Separation of calmodulin from calcium-activated protein kinase using calcium-dependent hydrophobic interaction chromatography

To determine whether a Ca2+-activated protein kinase is regulated by calmodulin, it is necessary to separate it from endogenous calmodulin and from protein kinase activity that is not calcium dependent. We describe here a procedure for achieving these goals using Ca2+-dependent hydrophobic interaction chromatography on phenyl Sepharose in combination with a pH change. The procedure is based on the observation that while calmodulin solubilized from apple fruit membranes binds to phenyl Sepharose in a Ca2+-dependent fashion at both pH 7.0 and 8.5, Ca2+-activated protein kinase from the same source only shows a Ca2+-dependent interaction above pH 7.5. The implications of this finding for the regulation of this Ca2+-activated protein kinase are briefly discussed.

Autophosphorylation of plasma membrane bound calcium calmodulin dependent protein kinase from pea seedlings and modification of catalytic activity by autophosphorylation

We have previously shown that pea seedling plasma membrane contains a protein kinase whose activity towards plasma membrane proteins is markedly increased by micromolar concentrations of calcium and calmodulin. The evidence in this paper suggests that this protein kinase autophosphorylates, that autophosphorylation is increased in a calcium and calmodulin dependent fashion and that prior autophosphorylation modifies activity towards an exogenous substrate. This protein kinase has a molecular weight of approximately 18,000 and is referred to as phosphoprotein18 (pp18).