Yue Jianbo, Ferrell James E
Stanford University School of Medicine, Department of Molecular Pharmacology, CCSR Room 3155, Stanford, CA 94305-5174, USA.
Mol Cell Biol. 2006 Jul;26(14):5300-9. doi: 10.1128/MCB.00273-06.
The protein kinase Mos is responsible for the activation of MEK1 and p42 mitogen-activated protein kinase during Xenopus oocyte maturation and during mitosis in Xenopus egg extracts. Here we show that the activation of Mos depends upon the phosphorylation of Ser 3, a residue previously implicated in the regulation of Mos stability; the dephosphorylation of Ser 105, a previously unidentified phosphorylation site conserved in Mos proteins; and the regulated dissociation of Mos from CK2beta. Mutation of Ser 3 to alanine and/or mutation of Ser 105 to glutamate produces a Mos protein that is defective for M-phase activation, as assessed by in vitro kinase assays, and defective for induction of oocyte maturation and maintenance of the spindle assembly checkpoint in extracts. Interestingly, Ser 105 is situated at the beginning of helix alphaC in the N-terminal lobe of the Mos kinase domain. Changes in the orientation of this helix have been previously implicated in the activation of Cdk2 and Src family tyrosine kinases. Our work suggests that Ser 105 dephosphorylation represents a novel mechanism for reorienting helix alphaC.
蛋白质激酶Mos在非洲爪蟾卵母细胞成熟过程以及非洲爪蟾卵提取物的有丝分裂过程中负责激活MEK1和p42丝裂原活化蛋白激酶。在此我们表明，Mos的激活依赖于Ser 3的磷酸化，Ser 3是一个先前被认为与Mos稳定性调节有关的残基；依赖于Ser 105的去磷酸化，Ser 105是Mos蛋白中一个先前未被鉴定的保守磷酸化位点；还依赖于Mos与CK2β的调控解离。将Ser 3突变为丙氨酸和/或将Ser 105突变为谷氨酸会产生一种Mos蛋白，通过体外激酶分析评估，该蛋白在M期激活方面存在缺陷，在提取物中诱导卵母细胞成熟和维持纺锤体组装检查点方面也存在缺陷。有趣的是，Ser 105位于Mos激酶结构域N端叶中αC螺旋的起始处。该螺旋方向的改变先前已被认为与Cdk2和Src家族酪氨酸激酶的激活有关。我们的研究表明，Ser 105去磷酸化代表了一种重新定向αC螺旋的新机制。
