title: Phosphorylation of high-mobility-group proteins by the calcium-phospholipid-dependent protein kinase and the cyclic AMP-dependent protein kinase.
abstract: Purified lamb thymus high-mobility-group (HMG) proteins 1, 2, and 17 have been investigated as potential substrates for the Ca2+-phospholipid-dependent protein kinase and the cAMP-dependent protein kinase. HMG proteins 1, 2, and 17 are phosphorylated by the Ca2+-phospholipid-dependent protein kinase; the reactions are totally Ca2+ and lipid dependent and are not inhibited by the inhibitor protein of the cAMP-dependent protein kinase. HMG 17 is phosphorylated predominantly in a single seryl residue, Ser 24 in the sequence Gln-Arg-Arg-Ser 24-Ala-Arg-Leu-Ser 28-Ala-Lys, with the second seryl moiety, Ser 28, modified to a markedly lesser degree. HMGs 1 and 2 are also phosphorylated in only seryl residues but with each there are multiple phosphorylation sites. HMG 17, but not HMG 1 or 2, is also phosphorylated by the cAMP-dependent protein kinase with the site phosphorylated being the minor of the two phosphorylated by the Ca2+-phospholipid-dependent protein kinase; the Km for phosphorylation by the cAMP-dependent enzyme is 50-fold higher than that by the Ca2+-phospholipid-dependent enzyme. HMG 17 is an equally effective substrate for the Ca2+-phospholipid-dependent protein kinase either as the pure protein or bound to nucleosomes. Preliminary evidence has indicated that lamb thymus HMG 14 is also a substrate for the Ca2+-phospholipid-dependent enzyme. It is phosphorylated with a Km similar to that of HMG 17 (4-6 microM), and a comparison of tryptic peptides suggests that it is phosphorylated in a site that is homologous with Ser 24 of HMG 17 and distinct from the sites phosphorylated by the cAMP-dependent protein kinase.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D006367:HeLa Cells / Q000378:metabolism; D006609:High Mobility Group Proteins / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D009707:Nucleosomes / Q000378:metabolism; D010446:Peptide Fragments / Q000032:analysis; D010766:Phosphorylation; D011493:Protein Kinase C; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D012756:Sheep; D013950:Thymus Gland; D014357:Trypsin
chemical_list: D006609:High Mobility Group Proteins; D009707:Nucleosomes; D010446:Peptide Fragments; D011494:Protein Kinases; D011493:Protein Kinase C; D014357:Trypsin