Xie X, Gu Y, Fox T, Coll J T, Fleming M A, Markland W, Caron P R, Wilson K P, Su M S
Vertex Pharmaceuticals Incorporated, Cambridge, MA 02139-4211, USA.
Structure. 1998 Aug 15;6(8):983-91. doi: 10.1016/s0969-2126(98)00100-2.
The c-Jun N-terminal kinases (JNKs) are members of the mitogen-activated protein (MAP) kinase family, and regulate signal transduction in response to environmental stress. Activation and nuclear localization of JNK3, a neuronal-specific isoform of JNK, has been associated with hypoxic and ischemic damage of CA1 neurons in the hippocampus. Knockout mice lacking JNK3 showed reduced apoptosis of hippocampal neurons and reduced seizure induced by kainic acid, a glutamate-receptor agonist. Thus, JNK3 may be important in the pathology of neurological disorders and is of significant medical interest.
We report here the structure of unphosphorylated JNK3 in complex with adenylyl imidodiphosphate, an ATP analog. JNK3 has a typical kinase fold, with the ATP-binding site situated within a cleft between the N- and C-terminal domains. In contrast to other known MAP kinase structures, the ATP-binding site of JNK3 is well ordered; the glycine-rich nucleotide-binding sequence forms a beta-strand-turn-beta-strand structure over the nucleotide. Unphosphorylated JNK3 assumes an open conformation, in which the N- and C-terminal domains are twisted apart relative to their positions in cAMP-dependent protein kinase. The rotation leads to the misalignment of some of the catalytic residues. The phosphorylation lip of JNK3 partially blocks the substrate-binding site.
This is the first JNK structure to be determined, providing a unique opportunity to compare structures from the three MAP kinase subfamilies. The structure reveals atomic-level details of the shape of JNK3 and the interactions between the kinase and the nucleotide. The misalignment of catalytic residues and occlusion of the active site by the phosphorylation lip may account for the low activity of unphosphorylated JNK3. The structure provides a framework for understanding the substrate specificity of different JNK isoforms, and should aid the design of selective JNK3 inhibitors.
c-Jun氨基末端激酶（JNKs）是丝裂原活化蛋白（MAP）激酶家族的成员，可调节对环境应激的信号转导。JNK的神经元特异性亚型JNK3的激活和核定位与海马体CA1神经元的缺氧和缺血性损伤有关。缺乏JNK3的基因敲除小鼠海马神经元凋亡减少，且由谷氨酸受体激动剂海藻酸诱导的癫痫发作减少。因此，JNK3可能在神经疾病的病理过程中起重要作用，具有重大医学研究价值。
我们在此报告未磷酸化的JNK3与腺苷酰亚胺二磷酸（一种ATP类似物）复合物的结构。JNK3具有典型的激酶折叠结构，ATP结合位点位于N端和C端结构域之间的裂隙内。与其他已知的MAP激酶结构不同，JNK3的ATP结合位点排列有序；富含甘氨酸的核苷酸结合序列在核苷酸上方形成β链-转角-β链结构。未磷酸化的JNK3呈开放构象，其中N端和C端结构域相对于它们在cAMP依赖性蛋白激酶中的位置扭曲分开。这种旋转导致一些催化残基错位。JNK3的磷酸化环部分阻断了底物结合位点。
这是首个被确定的JNK结构，为比较三个MAP激酶亚家族的结构提供了独特机会。该结构揭示了JNK3形状以及激酶与核苷酸之间相互作用的原子水平细节。催化残基的错位和磷酸化环对活性位点的封闭可能解释了未磷酸化JNK3的低活性。该结构为理解不同JNK亚型的底物特异性提供了框架，应有助于设计选择性JNK3抑制剂。
