Phosphorylation of high-mobility-group proteins by the calcium-phospholipid-dependent protein kinase and the cyclic AMP-dependent protein kinase

C. Ramachandran, P. Yau, E. M. Bradbury, G. Shyamala, H. Yasuda, D. A. Walsh

Research output: Contribution to journalArticle

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 K(m) 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 K(m) similar to that of HMG 17 (4-6 μm), 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.

Original languageEnglish (US)
Pages (from-to)13495-13503
Number of pages9
JournalJournal of Biological Chemistry
Volume259
Issue number21
StatePublished - Dec 1 1984
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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