Identification of the sites on rabbit skeletal muscle protein phosphatase inhibitor-2 phosphorylated by casein kinase-II.
Inhibitor-2 was phosphorylated by casein kinase-II in vitro at a rate similar to that of glycogen synthase, a physiological substrate of this protein kinase. The major phosphorylation sites were identified as serines-86, -120 and -121, the peptide containing serines-120 and -121 being labelled about 2.5-fold more rapidly than that containing serine-86. The 13 residues C-terminal to serine-121 (SGEEDSDLSPEERE) contain seven acidic amino acids, while the six residues following serine-86 (SDTETTE) contain three. These results are consistent with the known specificity requirements of casein kinase-II. The three serines are C-terminal to the threonine (residue 72) whose phosphorylation by glycogen synthase kinase-3 is potentiated by prior phosphorylation with casein kinase-II. This reinforces the view that a C-terminal phosphoserine residue is important for the specificity of glycogen synthase kinase-3. Identification of the residues phosphorylated by casein kinase-II will facilitate further studies on the in vivo phosphorylation state of inhibitor-2.
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D047388:Casein Kinases; D002851:Chromatography, High Pressure Liquid; D038341:Glycogen Synthase Kinases; D009132:Muscles / Q000201:enzymology*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D011817:Rabbits; D013329:Structure-Activity Relationship; D014357:Trypsin / Q000378:metabolism; D000097847:Protein Phosphatase Inhibitory Proteins
D017871:Calcium-Calmodulin-Dependent Protein Kinases; D047388:Casein Kinases; D038341:Glycogen Synthase Kinases; D011494:Protein Kinases; D011506:Proteins; D014357:Trypsin; C024833:protein phosphatase inhibitor-2; D000097847:Protein Phosphatase Inhibitory Proteins