Niefind Karsten, Yde Christina W, Ermakova Inessa, Issinger Olaf-Georg
Universität zu Köln, Institut für Biochemie, Zülpicher Strasse 47, D-50674 Köln, Germany.
J Mol Biol. 2007 Jul 13;370(3):427-38. doi: 10.1016/j.jmb.2007.04.068. Epub 2007 May 5.
CK2alpha is the catalytic subunit of protein kinase CK2 and a member of the CMGC family of eukaryotic protein kinases like the cyclin-dependent kinases, the MAP kinases and glycogen-synthase kinase 3. We present here a 1.6 A resolution crystal structure of a fully active C-terminal deletion mutant of human CK2alpha liganded by two sulfate ions, and we compare this structure systematically with representative structures of related CMGC kinases. The two sulfate anions occupy binding pockets at the activation segment and provide the structural basis of the acidic consensus sequence S/T-D/E-X-D/E that governs substrate recognition by CK2. The anion binding sites are conserved among those CMGC kinases. In most cases they are neutralized by phosphorylation of a neighbouring threonine or tyrosine side-chain, which triggers conformational changes for regulatory purposes. CK2alpha, however, lacks both phosphorylation sites at the activation segment and structural plasticity. Here the anion binding sites are functionally changed from regulation to substrate recognition. These findings underline the exceptional role of CK2alpha as a constitutively active enzyme within a family of strictly controlled protein kinases.
CK2α是蛋白激酶CK2的催化亚基，是真核蛋白激酶CMGC家族的成员，与细胞周期蛋白依赖性激酶、丝裂原活化蛋白激酶和糖原合酶激酶3同属该家族。我们在此展示了人CK2α一个完全活性的C末端缺失突变体与两个硫酸根离子结合后的1.6埃分辨率晶体结构，并将此结构与相关CMGC激酶的代表性结构进行了系统比较。这两个硫酸根阴离子占据了激活片段处的结合口袋，并为酸性共有序列S/T-D/E-X-D/E提供了结构基础，该序列决定了CK2对底物的识别。阴离子结合位点在那些CMGC激酶中是保守的。在大多数情况下，它们会被相邻苏氨酸或酪氨酸侧链的磷酸化中和，从而触发构象变化以实现调节目的。然而，CK2α在激活片段处既没有磷酸化位点，也缺乏结构可塑性。在这里，阴离子结合位点在功能上从调节转变为底物识别。这些发现突出了CK2α在一个严格受控的蛋白激酶家族中作为组成型活性酶的特殊作用。
