Full-length myotonin protein kinase (72 kDa) displays serine kinase activity.
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.
Timchenko
L
L
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA.
Nastainczyk
W
W
Schneider
T
T
Patel
B
B
Hofmann
F
F
Caskey
C T
CT
D000595:Amino Acid Sequence; D015153:Blotting, Western; D020746:Calcium Channels, L-Type; D002460:Cell Line; D006801:Humans; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000378:metabolism; D065636:Myotonin-Protein Kinase; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D013379:Substrate Specificity
D020746:Calcium Channels, L-Type; C585517:DMPK protein, human; D009124:Muscle Proteins; D011494:Protein Kinases; D065636:Myotonin-Protein Kinase; D017346:Protein Serine-Threonine Kinases