Multiple steps of phosphorylation of activated rhodopsin can account for the reproducibility of vertebrate rod single-photon responses.
Multiple steps of phosphorylation of activated rhodopsin can account for the reproducibility of vertebrate rod single-photon responses.
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DOI：
10.1085/jgp.200308832
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发表时间：
2003-10
期刊：
影响因子：
--
通讯作者：
Lamb TD
中科院分区：
文献类型：
--
作者：
Hamer RD;Nicholas SC;Tranchina D;Liebman PA;Lamb TD
如果异构化视紫红质 (R*) 在单个无记忆步骤中失活，并且没有其他降低变异性的机制可用，那么脊椎动物视杆细胞中的单光子响应 (SPR) 的变异性比预期的要小得多。我们提出了一个新的随机模型，其核心是随着 R* 的每次磷酸化，R* 活性连续下降，并伴随着视紫红质抑制蛋白 (Arr) 猝灭 R* 的概率增加（Gibson, S.K., J.H. Parkes, and P.A. Liebman. 2000. Biochemistry. 39:5738–5749.）。我们通过暗光闪光响应的蒙特卡罗模拟来评估模型，并将从中得出的响应统计数据与从经验暗光闪光数据获得的响应统计数据进行比较（Whitlock，G.G.和T.D. Lamb. 1999. Neuron. 23:337–351.）。该模型考虑了 SPR 再现性的四种定量测量。它还再现了通过改变核苷酸水平获得的视杆反应的定性特征，因此与以下结论相矛盾：这种反应意味着磷酸化不能主导 R* 失活（Rieke, F., and D.A. Baylor. 1998a. Biophys. J. 75:1836–1857; Field, G.D., and F. Rieke. 2002. Neuron. 35：733-747。）。此外，该模型能够重现从小鼠杆中获得的 SPR 的显着定性特征，这些杆经过基因改造，具有 R* 失活或 Ca2+ 反馈禁用的特定途径。我们提出的理论分析表明，SPR 下面积的变异性可估计综合 R* 活性的变异性，并且可以提供 R* 失活步骤数量的有效衡量标准。我们表明，SPR 幅度的可变性和 SPR 持续时间之间存在迄今为止未被认识到的权衡，这主要取决于 R* 失活动力学相对于级联中下游反应的净动力学。由于这种依赖性，SPR 幅度和持续时间的变异性都不能提供对整合 R* 活性的潜在变异性的可靠估计，并且不能用于估计 R* 失活步骤的最小数量。我们得出的结论是，R* 活性的多重磷酸化依赖性减弱（使用 Arr 猝灭）可以赋予观察到的杆 SPR 的再现性；没有迫切需要在 R* 中引发一系列非磷酸化依赖性状态变化（如 Rieke, F., and D.A. Baylor. 1998a. Biophys. J. 75:1836–1857; Field, G.D., and F. Rieke. 2002. Neuron. 35:733–747.）。我们的分析以及其他人的数据和建模（Rieke, F., and D.A. Baylor. 1998a. Biophys. J. 75:1836–1857; Field, G.D., and F. Rieke. 2002. Neuron. 35:733–747.）也强烈反对反馈（包括 Ca2+-反馈）或下游任何分子种类的耗尽。 R* 是 SPR 重现性的主要原因。
Single-photon responses (SPRs) in vertebrate rods are considerably less variable than expected if isomerized rhodopsin (R*) inactivated in a single, memoryless step, and no other variability-reducing mechanisms were available. We present a new stochastic model, the core of which is the successive ratcheting down of R* activity, and a concomitant increase in the probability of quenching of R* by arrestin (Arr), with each phosphorylation of R* (Gibson, S.K., J.H. Parkes, and P.A. Liebman. 2000. Biochemistry. 39:5738–5749.). We evaluated the model by means of Monte-Carlo simulations of dim-flash responses, and compared the response statistics derived from them with those obtained from empirical dim-flash data (Whitlock, G.G., and T.D. Lamb. 1999. Neuron. 23:337–351.). The model accounts for four quantitative measures of SPR reproducibility. It also reproduces qualitative features of rod responses obtained with altered nucleotide levels, and thus contradicts the conclusion that such responses imply that phosphorylation cannot dominate R* inactivation (Rieke, F., and D.A. Baylor. 1998a. Biophys. J. 75:1836–1857; Field, G.D., and F. Rieke. 2002. Neuron. 35:733–747.). Moreover, the model is able to reproduce the salient qualitative features of SPRs obtained from mouse rods that had been genetically modified with specific pathways of R* inactivation or Ca2+ feedback disabled. We present a theoretical analysis showing that the variability of the area under the SPR estimates the variability of integrated R* activity, and can provide a valid gauge of the number of R* inactivation steps. We show that there is a heretofore unappreciated tradeoff between variability of SPR amplitude and SPR duration that depends critically on the kinetics of inactivation of R* relative to the net kinetics of the downstream reactions in the cascade. Because of this dependence, neither the variability of SPR amplitude nor duration provides a reliable estimate of the underlying variability of integrated R* activity, and cannot be used to estimate the minimum number of R* inactivation steps. We conclude that multiple phosphorylation-dependent decrements in R* activity (with Arr-quench) can confer the observed reproducibility of rod SPRs; there is no compelling need to invoke a long series of non-phosphorylation dependent state changes in R* (as in Rieke, F., and D.A. Baylor. 1998a. Biophys. J. 75:1836–1857; Field, G.D., and F. Rieke. 2002. Neuron. 35:733–747.). Our analyses, plus data and modeling of others (Rieke, F., and D.A. Baylor. 1998a. Biophys. J. 75:1836–1857; Field, G.D., and F. Rieke. 2002. Neuron. 35:733–747.), also argue strongly against either feedback (including Ca2+-feedback) or depletion of any molecular species downstream to R* as the dominant cause of SPR reproducibility.
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影响因子：
1.8
作者：
EBREY, TG
通讯作者：
EBREY, TG
影响因子：
2.9
作者：
Gibson, SK;Parkes, JH;Liebman, PA
通讯作者：
Liebman, PA
影响因子：
1.9
作者：
Haynes, LW;Stotz, SC
通讯作者：
Stotz, SC
影响因子：
1.8
作者：
Hurley, JB;Spencer, M;Niemi, GA
通讯作者：
Niemi, GA
影响因子：
16.2
作者：
Kennedy, MJ;Lee, KA;Hurley, JB
通讯作者：
Hurley, JB