Marin O, Meggio F, Draetta G, Pinna L A
Dipartimento di Chimica Biologica, Università di Padova, Italy.
FEBS Lett. 1992 Apr 13;301(1):111-4. doi: 10.1016/0014-5793(92)80221-2.
Two series of synthetic peptides that reproduce the amino- and carboxyl-terminal segments of the beta-subunit of casein kinase-2, including the sites phosphorylated by CK2 and cdc2 kinase, respectively, have been used as model substrates for these enzymes. The N-terminal peptide beta(1-9), MSSSEEVSW, is readily phosphorylated by CK2 but not all by cdc2. The opposite is true of the C-terminal peptide beta(206-215), NFKSPVKTIR, whose Ser-4 is a good target for cdc2 while being unaffected by CK2. The individual substitutions of Pro-5 and Lys-7 in the latter peptide with Gly and Ala (or Glu), respectively, prevent its phosphorylation by cdc2, whereas the substitution of Lys-3 with Ala is well tolerated and the substitution of the target Ser with Thr actually improves phosphorylation. Thus the consensus sequence for cdc2 is shown to be X-S-P-X-K. Such a requirement for a basic residue at position +3 is opposite to that of CK2 whose consensus sequence (S-X-X-E/D/Yp/Sp) includes an acidic residue at the same position. Moreover the motif Ser-Pro is detrimental for CK2, preventing the phosphorylation of otherwise suitable peptides. These observations would rule out the possibility that the site specificity of CK2 might overlap with that of cdc2 and possibly of other Pro-directed protein kinases.
已使用两组合成肽作为这些酶的模型底物，这两组肽分别重现了酪蛋白激酶2β亚基的氨基末端和羧基末端片段，包括分别被CK2和cdc2激酶磷酸化的位点。N端肽β(1 - 9)，MSSSEEVSW，很容易被CK2磷酸化，但完全不会被cdc2磷酸化。C端肽β(206 - 215)，NFKSPVKTIR则相反，其Ser - 4是cdc2的良好磷酸化靶点，而不受CK2影响。后一种肽中Pro - 5和Lys - 7分别被Gly和Ala（或Glu）单独取代，会阻止其被cdc2磷酸化，而Lys - 3被Ala取代则耐受性良好，靶点Ser被Thr取代实际上会增强磷酸化作用。因此，cdc2的共有序列显示为X - S - P - X - K。在 +3 位对碱性残基的这种要求与CK2相反，CK2的共有序列（S - X - X - E/D/Yp/Sp）在相同位置包含一个酸性残基。此外，Ser - Pro基序对CK2不利，会阻止其他合适肽段的磷酸化。这些观察结果排除了CK2的位点特异性可能与cdc2以及可能与其他脯氨酸导向蛋白激酶的位点特异性重叠的可能性。
