Submitted to: American Society of Plant Physiologists Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/31/2001
Publication Date: N/A
Citation: N/A Interpretive Summary:
Technical Abstract: Light dependent reversible phosphorylation of several chloroplast Photosystem II (PSII) proteins is well known. However, little is known about the kinases responsible for their phosphorylation. Using as substrate a synthetic peptide mimicking the N-terminus where D1 undergoes phosphorylation, we have isolated, identified and characterized a thylakoidal protein kinase. The putative D1 kinase is an extrinsic membrane protein of 50 kD with an optimum pH of 7.4, isoelectric point of 5.5, and preference for manganese cations. We sequenced several tryptic fragments of the protein, based on which we synthesized degenerate oligonucleotide primers to clone the gene. The cDNA sequence predicts a protein kinase (CDPK) with a mass of 59 kD, a size compatible with processing of a primary translation product to produce a mature protein like that recovered from purification of the rice kinase. One of the CDPK isoforms from Spirodela but not the rice CDPK is imported into intact pea chloroplasts. Spirodela kinase expressed in E. coli as an N-terminal 6-His fusion protein phosphorylated the N-terminal synthetic D1 peptide, but not LHCII or Rubisco peptides. Acetylated D1 peptide was as good a substrate as the unacetylated peptide. Further analysis is in progress to study the role of CDPK in chloroplast function.