2-STATE MODEL FOR BACTERIAL CHEMORECEPTOR PROTEINS - THE ROLE OF MULTIPLE METHYLATION
2-STATE MODEL FOR BACTERIAL CHEMORECEPTOR PROTEINS - THE ROLE OF MULTIPLE METHYLATION
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DOI：
10.1016/0022-2836(84)90494-7
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发表时间：
1984-01-01
影响因子：
5.6
通讯作者：
HONDA, H
中科院分区：
文献类型：
--
作者：
ASAKURA, S;HONDA, H
为了帮助理解细菌的趋化反应的兴奋和适应，提出了一个简单的2状态模型受体蛋白（甲基接受趋化蛋白），根据证据，他们经历多个甲基化优先顺序。该模型包括几个假设。受体蛋白在S和T两种构象之间快速平衡，随着甲基数量的增加，平衡向T形式转移。引诱剂与受体的S型结合，驱避剂与T型结合，两类配体根据质量作用定律改变S/T平衡。S型受体按一定的顺序接受1对1的甲基，而T型受体则按相反的顺序释放甲基。甲基化和去甲基化是缓慢的反应，甲基总数的变化滞后于S/T平衡的变化。细菌在任何时刻的游动模式是由受体在两种构象之间的分配决定的，翻滚频率是受体总T分数的单调递增函数。该模型表明，如果受体满足其平衡常数和动力学常数的两组关系，它可以在很大的配体浓度范围内保持稳态总T分数基本恒定，使细胞能够适应化学环境的大变化。配体浓度的逐步变化导致总T分数的快速变化（激发），随后是一个缓慢的松弛过程（适应）。计算机模拟了整个反应过程，采用每个分子有6个甲基化位点的受体，并假设简单的参数集。该结果与已发表的受体甲基化数据和细菌化学反应的各种观察结果大致一致。受体的多重甲基化被证明是细胞对环境变化做出敏感反应所必需的。
To help understand the bacterial chemotactic response of excitation and adaptation, a simple 2-state model is proposed for receptor proteins (methyl-accepting chemotaxis proteins), in the light of evidence that they undergo multiple methylation in a preferred order. The model includes several assumptions. The receptor protein is in rapid equilibrium between 2 conformations, S and T, and the equilibrium shifts towards the T form as the number of methyl groups increases. Attractants bind to the S form of the receptor, repellents bind to the T form, and both classes of ligand shift the S/T equilibrium according to the mass-action law. The S form of the receptor accepts methyl groups 1 by 1 in a definite order, while the T form releases the methyl groups in the reverse order. Methylation and demethylation are slow reactions, and changes in the total number of methyl groups lag behind shifts in the S/T equilibrium. The pattern of bacterial swimming at any moment is determined by the partition of the receptor between the 2 conformations, with tumbling frequency being a monotonically increasing function of the total T fraction of the receptor. This model shows that, if the receptor satisfies 2 sets of relationships imposed on its equilibrium and kinetic constants, it can maintain the steady-state total T fraction essentially constant over a broad range of ligand concentration, enabling cells to adapt to large changes in chemical environment. A stepwise change in ligand concentration leads to a rapid change in the total T fraction (excitation), followed by a slow relaxation process (adaptation). Computer simulations were made of the whole response process, employing a receptor with 6 methylation sites per molecule and assuming simple sets of parameters. The results are in general agreement with published data on receptor methylation and with a variety of observations of bacterial chemoresponse. Multiple methylation of the receptor proves to be necessary for the cells to respond sensitively to environmental changes.