Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 1, 2001
Publication Date: N/A
Technical Abstract:
Phosphorylation of several chloroplast Photosystem II (PSII) proteins is well known. However, little is known about the kinases catalyzing the phosphorylation. We have isolated, identified and characterized a thylakoidal protein kinase that phosphorylates the D1 protein. 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. The N-terminus of the purified protein was blocked. Therefore, several tryptic fragments of the protein were sequenced, based on which we synthesized degenerate oligonucleotide primers to clone the gene from a cDNA library made to Spirodela RNAs. The cDNA sequence predicts a protein kinase with a mass of 59 kD based on the entire open reading frame. This size is compatible with processing of a primary translation product to produce a mature protein like that recovered from purification. The protein kinase gene identified shows strong sequence similarities to members of the family of calcium dependent protein kinases. 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.
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