Tio Chong Wai, Omerza Gregory, Phillips Timothy, Lou Hua Jane, Turk Benjamin E, Winter Edward
Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
Department of Pharmacology, Yale University, New Haven, Connecticut, USA.
Mol Cell Biol. 2017 May 2;37(10). doi: 10.1128/MCB.00607-16. Print 2017 May 15.
Smk1 is a meiosis-specific mitogen-activated protein kinase (MAPK) in that couples spore morphogenesis to the completion of chromosome segregation. Similar to other MAPKs, Smk1 is controlled by phosphorylation of a threonine (T) and a tyrosine (Y) in its activation loop. However, it is not activated by a dual-specificity MAPK kinase. Instead, T207 in Smk1's activation loop is phosphorylated by the cyclin-dependent kinase (CDK)-activating kinase (Cak1), and Y209 is autophosphorylated in an intramolecular reaction that requires the meiosis-specific protein Ssp2. In this study, we show that Smk1 is catalytically inert unless it is bound by Ssp2. While Ssp2 binding activates Smk1 by a mechanism that is independent of activation loop phosphorylation, binding also triggers autophosphorylation of Y209 in Smk1, which, along with Cak1-mediated phosphorylation of T207, further activates the kinase. Autophosphorylation of Smk1 on Y209 also appears to modify the specificity of the MAPK by suppressing Y kinase and enhancing S/T kinase activity. We also found that the phosphoconsensus motif preference of Ssp2/Smk1 is more extensive than that of other characterized MAPKs. This study therefore defines a novel mechanism of MAPK activation requiring binding of an activator and also shows that MAPKs can be diversified to recognize unique phosphorylation motifs.
Smk1是一种减数分裂特异性丝裂原活化蛋白激酶（MAPK），它将孢子形态发生与染色体分离的完成联系起来。与其他MAPK类似，Smk1由其激活环中的苏氨酸（T）和酪氨酸（Y）磷酸化控制。然而，它不是由双特异性MAPK激酶激活的。相反，Smk1激活环中的T207由细胞周期蛋白依赖性激酶（CDK）激活激酶（Cak1）磷酸化，Y209在需要减数分裂特异性蛋白Ssp2的分子内反应中进行自磷酸化。在本研究中，我们表明Smk1在未与Ssp2结合时催化惰性。虽然Ssp2结合通过一种独立于激活环磷酸化的机制激活Smk1，但结合也会触发Smk1中Y209的自磷酸化，这与Cak1介导的T207磷酸化一起进一步激活该激酶。Smk1在Y209上的自磷酸化似乎也通过抑制Y激酶和增强S/T激酶活性来改变MAPK的特异性。我们还发现Ssp2/Smk1的磷酸化共有基序偏好比其他已表征的MAPK更广泛。因此，本研究定义了一种需要激活剂结合的MAPK激活新机制，并且还表明MAPK可以多样化以识别独特的磷酸化基序。
