Phosphopeptide mapping of Avena phytochrome phosphorylated by protein kinases in vitro.
We previously demonstrated that protein kinases are useful probes of conformational changes that occur upon photoconversion of phytochrome [Wong, Y.-S., Cheng, H.-C., Walsh, D. A., & Lagarias, J. C. (1986) J. Biol. Chem. 261, 12089-12097]. Here we present phosphopeptide analyses of oat phytochrome phosphorylated by three mammalian protein kinases and by a polycation-stimulated, phytochrome-associated protein kinase. Phosphorylation of the Pr form by the cAMP-dependent protein kinase occurs predominantly on Ser17 while Ser598 is the preferred phosphorylation site on Pfr. The cGMP-dependent and Ca2(+)-activated, phospholipid-dependent protein kinases, which phosphorylate only the Pr form of phytochrome, recognize the same region on the phytochrome polypeptide as the cAMP-dependent protein kinase. Polycation-stimulated phytochrome phosphorylation reveals that, in contrast to the mammalian enzymes, the plant kinase recognizes the serine-rich, blocked N-terminus of phytochrome. The potential regulatory role of phytochrome phosphorylation, particularly in the structurally conserved serine/threonine-rich N-terminal region of the phytochrome polypeptide, is suggested by these results.
McMichael
R W
RW
Department of Biochemistry and Biophysics, University of California, Davis 95616.
Lagarias
J C
JC
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002417:Cattle; D002523:Edible Grain; D006868:Hydrolysis; D066298:In Vitro Techniques; D008168:Lung / Q000201:enzymology*; D010449:Peptide Mapping; D010748:Phosphopeptides / Q000032:analysis*; D010766:Phosphorylation; D010834:Phytochrome / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D011487:Protein Conformation; D011494:Protein Kinases / Q000378:metabolism*
D000596:Amino Acids; D010748:Phosphopeptides; D010940:Plant Proteins; D010834:Phytochrome; D011494:Protein Kinases