Phosphorylation of phosvitin by casein kinase-2 provides the evidence that phosphoserines can replace carboxylic amino acids as specificity determinants.
The consensus sequence of casein kinase-2 consists of a serine (threonine) followed by a cluster of glutamic and/or aspartic acids, the one at position +3 playing an especially crucial role (Marin et al., (1986) Eur. J. Biochem. 160, 239-244 and Kuenzel et al. (1987) J. Biol. Chem. 262, 9136-9140). None of the 123 serines of the main phosvitin component (34 kDa) fulfils such a requirement (Byrne et al. (1984) Biochemistry 23, 4275-4279), rather, most of them are clustered into stretches of up to 14 entirely phosphorylated residues. Three out of the four threonines lie close to the N-terminal side of such phosphoseryl blocks. Here we show that native 34 kDa phosvitin is a poor substrate of casein kinase-2, its radiolabeling occurring mostly at threonine residue(s); a very slight (1%) previous dephosphorylation with acid phosphatase converts phosvitin into an excellent substrate for casein kinase-2, its phosphorylation occurring almost exclusively at serine residues. Extensive dephosphorylation however (greater than 40%) reduces the phosphorylation efficiency of casein kinase-2. These results show that phosphoserine residues can replace carboxylic residues as specificity determinants for casein kinase-2.
D000596:Amino Acids / Q000378:metabolism*; D001224:Aspartic Acid / Q000378:metabolism; D047388:Casein Kinases; D004527:Egg Proteins / Q000378:metabolism*; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism*; D010769:Phosphothreonine / Q000378:metabolism; D010774:Phosvitin / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D012694:Serine / Q000031:analogs & derivatives*; D013379:Substrate Specificity
D000596:Amino Acids; D004527:Egg Proteins; D005971:Glutamates; D010769:Phosphothreonine; D010768:Phosphoserine; D001224:Aspartic Acid; D018698:Glutamic Acid; D012694:Serine; D010774:Phosvitin; D011494:Protein Kinases; D047388:Casein Kinases