Redox-Based Probes for Protein Tyrosine Phosphatases
Redox-Based Probes for Protein Tyrosine Phosphatases
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DOI：
10.1002/anie.201007871
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Carroll, Kate S.
中科院分区：
文献类型：
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作者：
Leonard, Stephen E.;Garcia, Francisco J.;Carroll, Kate S.
在过去的二十年里，已经确定生长因子、细胞因子和许多其他配体通过其相应的膜受体触发非吞噬细胞中过氧化氢 (H2O2) 的产生。 [1]这种 H2O2 的产生已被证明可以调节许多基本的细胞过程，包括生长、分化、粘附、迁移、衰老和自噬。 [2]一旦形成，H2O2 就会促进膜受体的自身磷酸化并诱导信号级联反应。 Finkel 和 Rhee 实验室的里程碑式出版物首次证明了活性氧 (ROS) 生长因子受体介导的信号转导的重要作用。 [3]如图 1 所示，配体刺激会导致 H2O2 瞬时爆发，并导致许多蛋白质（包括生长因子受体本身）的酪氨酸磷酸化净增加。 [4]同样，应用过氧化物清除剂（例如 N-乙酰半胱氨酸或过氧化氢酶）可抑制配体诱导的酪氨酸磷酸化。在很大程度上，这些效应被认为是由蛋白酪氨酸磷酸酶 (PTP) 的氧化抑制引起的，PTP 充当蛋白酪氨酸激酶的拮抗剂并使膜受体恢复到静息状态。 [5] PTP 超家族约有 80 个成员，包括酪氨酸 (Tyr) 特异性酶和双特异性磷酸酶 (DSP)，它们也识别丝氨酸 (Ser) 和苏氨酸 (Thr)。 [6] PTP 的催化活性取决于位于活性位点袋底部的保守特征基序 [His-Cys-(X) 5-Arg-(Ser/Thr)]（His= 组氨酸，Arg= 精氨酸；X= 任何残基）内的不变活性位点半胱氨酸 (Cys)。 [7]由于活性位点的环境，催化的 Cys 残基表现出非常低的 pKa（4.5 至 5.5），并且在生理 pH 下以硫醇阴离子形式存在。低 pKa 有助于增强该残基的亲核性，但也使其易于氧化和酶失活。 [8]因此，PTP 的氧化抑制促进磷酸化依赖性信号级联反应。生化证据表明，接触 H2O2 后，催化性 Cys 残基会转化为次磺酸形式，导致 PTP 失活（图 1）。 [9]这种氧代形式可以与主链酰胺反应形成经典 PTP 的环状硫基酰胺，或与 DSP 中的相邻硫醇反应形成分子内二硫化物。 [10] PTP 的活性可以通过细胞抗氧化剂（例如硫氧还蛋白和谷氧还蛋白还原系统）的作用来恢复。 [5, 11] 因此，催化 Cys 的氧化是可逆的，代表了 PTP 调节的动态机制。尽管图 1 中的模型得到了许多优秀研究的支持，但众所周知，PTP 与 H2O2 的反应速率比与过氧化还原酶（一种抗氧化酶）的等效反应慢约 105 倍。[9, 10] 这提出了一个问题：非酶促反应是否可以解释 PTP 中次磺酸的形成。[12]这种明显的差异可能反映了酶促 H2O2 生成需要在靠近 PTP 的地方发生的可能性，以便 H2O2 的浓度
Over the past two decades, it has been established that growth factors, cytokines, and a host of other ligands trigger the production of hydrogen peroxide (H2O2) in nonphagocytic cells through their corresponding membrane receptors.[1] Such H2O2 generation has been demonstrated to regulate many basic cellular processes including growth, differentiation, adhesion, migration, senescence, and autophagy.[2] Once formed, H2O2 promotes autophosphorylation of the membrane receptor and induction of the signaling cascade. Landmark publications from the Finkel and Rhee laboratories were the first to demonstrate an essential role for reactive oxygen species (ROS) growth factor receptor-mediated signal transduction.[3] As illustrated in Figure 1, ligand stimulation leads to a transient burst of H2O2 and a net increase in tyrosine phosphorylation of numerous proteins, including the growth factor receptor itself.[4] Likewise, application of peroxide scavengers such as N-acetyl cysteine or catalase inhibits ligand-induced tyrosine phosphorylation. In large part, these effects are believed to arise from oxidative inhibition of protein tyrosine phosphatases (PTPs), which function as antagonists of protein tyrosine kinases and return membrane receptors to their resting state.[5] There are about 80 members of the PTP superfamily, including the tyrosine (Tyr)-specific enzymes and dualspecificity phosphatases (DSPs), which also recognize serine (Ser) and threonine (Thr).[6] The catalytic activity of PTPs depends upon an invariant active site cysteine (Cys) within the conserved signature motif [His-Cys-(X) 5-Arg-(Ser/Thr)](His= histidine, Arg= arginine; X= any residue) located at the bottom of the active site pocket.[7] Owing to the environment of the active site, the catalytic Cys residue exhibits a remarkably low pKa (4.5 to 5.5) and is present as the thiolate anion at physiological pH. The low pKa serves to enhance the nucleophilicity of this residue, but also renders it susceptible to oxidation and enzymatic inactivation.[8] Consequently, oxidative inhibition of PTPs promotes phosphorylationdependent signaling cascades. Biochemical evidence indicates that upon exposure to H2O2, the catalytic Cys residue is converted into the sulfenic acid form and results in PTP inactivation (Figure 1).[9] This oxo form can react with a backbone amide to form a cyclic sulfenyl amide for classical PTPs or an adjacent thiol in DSPs to form an intramolecular disulfide.[10] The activity of PTPs can be restored through the action of cellular antioxidants, such as the thioredoxin and glutaredoxin reducing systems.[5, 11] Thus, oxidation of the catalytic Cys is reversible and represents a dynamic mechanism of PTP regulation. Although the model presented in Figure 1 is supported by a number of elegant studies, it is also well-known that the rate of reaction of a PTP with H2O2 is about 105 times slower than the equivalent reaction with peroxiredoxin, an antioxidant enzyme.[9, 10] This raises the question of whether a nonenzymatic reaction can account for the formation of the sulfenic acid in PTPs.[12] This apparent discrepancy may reflect the possibility that enzymatic H2O2 generation needs to occur in close proximity to PTPs so that the concentration of the