Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, PA 19107.
Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794.
Mol Biol Cell. 2018 Jan 1;29(1):66-74. doi: 10.1091/mbc.E17-07-0473. Epub 2017 Nov 8.
Smk1 is a meiosis-specific MAP kinase (MAPK) in budding yeast that is required for spore formation. It is localized to prospore membranes (PSMs), the structures that engulf haploid cells during meiosis II (MII). Similar to canonically activated MAPKs, Smk1 is controlled by phosphorylation of its activation-loop threonine (T) and tyrosine (Y). However, activation loop phosphorylation occurs via a noncanonical two-step mechanism in which 1) the cyclin-dependent kinase activating kinase Cak1 phosphorylaytes T207 during MI, and 2) Smk1 autophosphorylates Y209 as MII draws to a close. Autophosphorylation of Y209 and catalytic activity for substrates require Ssp2, a meiosis-specific protein that is translationally repressed until anaphase of MII. Ama1 is a meiosis-specific targeting subunit of the anaphase-promoting complex/cyclosome that regulates multiple steps in meiotic development, including exit from MII. Here, we show that Ama1 activates autophosphorylation of Smk1 on Y209 by promoting formation of the Ssp2/Smk1 complex at PSMs. These findings link meiotic exit to Smk1 activation and spore wall assembly.
Smk1 是芽殖酵母减数分裂特异性丝裂原活化蛋白激酶 (MAPK)，是孢子形成所必需的。它定位于孢子前膜 (PSM)，在减数分裂 II (MII) 期间吞噬单倍体细胞的结构。与经典激活的 MAPK 相似，Smk1 的激活环苏氨酸 (T) 和酪氨酸 (Y) 的磷酸化控制其活性。然而，激活环磷酸化通过非典型的两步机制发生，其中 1）细胞周期蛋白依赖性激酶激活激酶 Cak1 在 MI 期间磷酸化 T207，2）Smk1 在 MII 接近尾声时自身磷酸化 Y209。Y209 的自身磷酸化和对底物的催化活性需要 Ssp2，这是一种减数分裂特异性蛋白，直到 MII 的后期才被翻译抑制。Ama1 是有丝分裂促进复合物/环体的减数分裂特异性靶向亚基，调节减数分裂发育的多个步骤，包括从 MII 中退出。在这里，我们表明 Ama1 通过促进 Ssp2/Smk1 复合物在 PSM 上的形成来激活 Smk1 的 Y209 自身磷酸化。这些发现将减数分裂退出与 Smk1 激活和孢子壁组装联系起来。
