Full-length myotonin protein kinase (72 kDa) displays serine kinase activity

Proc Natl Acad Sci U S A. 1995 Jun 6;92(12):5366-70. doi: 10.1073/pnas.92.12.5366.


We describe the full-length (72 kDa) myotonin protein kinase (Mt-PK) and demonstrate its kinase activity. The 72-kDa protein corresponds to the translation product from the first in-frame AUG codon. This protein was found in the cytoplasmic fraction, whereas the previously reported 55-kDa protein was observed in nuclear extracts. Only the 72-kDa protein was phosphorylated by [32P]phosphate in normal human fibroblasts. To investigate the putative kinase activity of Mt-PK, a construct containing the full-length open reading frame of Mt-PK was expressed in bacterial cells. The recombinant Mt-PK autophosphorylates a Ser residue and phosphorylates the synthetic peptide Gly-Arg-Gly-Leu-Ser-Leu-Ser-Arg, which contains a Ser residue in the phosphorylation site. We examined phosphorylation of the voltage-dependent Ca(2+)-release channel, or dihydropyridine receptor (DHPR), by recombinant Mt-PK. We observed that the beta subunit of DHPR was phosphorylated in vitro by Mt-PK. A beta-subunit DHPR peptide containing some of the Ser residues predicted to be phosphorylated was synthesized and found to be a substrate for Mt-PK in vitro. We conclude that the 72-kDa Mt-PK has a protein kinase activity specific for Ser residues.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Blotting, Western
  • Calcium Channels, L-Type
  • Cell Line
  • Humans
  • Molecular Sequence Data
  • Muscle Proteins / metabolism
  • Myotonin-Protein Kinase
  • Phosphorylation
  • Protein Kinases / metabolism*
  • Protein Serine-Threonine Kinases / metabolism*
  • Substrate Specificity


  • Calcium Channels, L-Type
  • DMPK protein, human
  • Muscle Proteins
  • Protein Kinases
  • Myotonin-Protein Kinase
  • Protein Serine-Threonine Kinases