Cooperative Kinetics of the Glucan Phosphatase Starch Excess4
Cooperative Kinetics of the Glucan Phosphatase Starch Excess4
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DOI：
10.1021/acs.biochem.1c00307
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发表时间：
2021-07-28
期刊：
影响因子：
2.9
通讯作者：
Raththagala，Madushi
中科院分区：
文献类型：
--
作者：
Mak，Claudia A.;Weis，Kenyon;Raththagala，Madushi
葡聚糖磷酸酶是功能多样的双特异性磷酸酶（DSP）家族的成员。植物葡聚糖磷酸酶淀粉过量4（SEX4）结合和脱磷酸化葡聚糖，有助于叶绿体中的淀粉在夜间进行性降解。当SEX4作用于其复杂的生理学相关的葡聚糖底物时，对SEX4的复杂动力学知之甚少。因此，我们探索了SEX4对不溶性淀粉和可溶性支链淀粉葡聚糖底物的动力学。SEX4显示出稳健的活性和对支链淀粉的独特S形动力学响应，其特征在于希尔系数为2.77 ± 0.63，这是协同性的标志性特征。我们研究了这种正动力学协同性的基础，并确定SEX4碳水化合物结合模块（CBM）显着影响结合协同性和底物转化率。这些发现为SEX4在可逆淀粉磷酸化中的一个先前未知但重要的调节作用提供了见解，并进一步推进了我们对非典型动力学机制的理解。
Glucan phosphatases are members of a functionally diverse family of dual-specificity phosphatase (DSP) enzymes. The plant glucan phosphatase Starch Excess4 (SEX4) binds and dephosphorylates glucans, contributing to processive starch degradation in the chloroplast at night. Little is known about the complex kinetics of SEX4 when acting on its complex physiologically relevant glucan substrate. Therefore, we explored the kinetics of SEX4 against both insoluble starch and soluble amylopectin glucan substrates. SEX4 displays robust activity and a unique sigmoidal kinetic response to amylopectin, characterized by a Hill coefficient of 2.77 ± 0.63, a signature feature of cooperativity. We investigated the basis for this positive kinetic cooperativity and determined that the SEX4 carbohydrate-binding module (CBM) dramatically influences the binding cooperativity and substrate transformation rates. These findings provide insights into a previously unknown but important regulatory role for SEX4 in reversible starch phosphorylation and further advances our understanding of atypical kinetic mechanisms.