Directions for Optimization of Photosynthetic Carbon Fixation: RuBisCO's Efficiency May Not Be So Constrained After All.
Directions for Optimization of Photosynthetic Carbon Fixation: RuBisCO's Efficiency May Not Be So Constrained After All.
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DOI：
10.3389/fpls.2018.00183
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发表时间：
2018
影响因子：
5.6
通讯作者：
Gready JE
中科院分区：
文献类型：
--
作者：
Cummins PL;Kannappan B;Gready JE
普遍存在的酶核酮糖1，5-二磷酸羧化酶-加氧酶（RuBisCO）将大气中的二氧化碳固定在被大多数光合生物利用的卡尔文-本森循环内。尽管有这种核心作用，但RuBisCO的效率令人惊讶地挣扎，具有非常缓慢的产物周转率和受损的底物特异性，这些特征长期以来一直是一个谜，因为人们认为其效率处于强大的进化压力下。RuBisCO的底物特异性受到损害，因为它催化与大气中的氧气的侧固定反应;经验动力学结果显示相对特异性和低催化周转率之间的权衡趋势。虽然占主导地位的假设一直是活性位点的化学约束酶的进化，最近的研究RuBisCO的稳定性和适应性有牵连的竞争选择压力。阐明这些限制是至关重要的指导未来的研究，提高光合作用，目前的文献提出了怀疑的潜在有效性的定点诱变，以提高RuBisCO的效率。在这里，我们使用回归分析来量化从经验数据集获得的动力学参数之间的关系跨越了广泛的进化范围的RuBisCO。最重要的是，我们发现，从酶复合物的解离CO2的速率常数远高于以前的估计和相应的催化速率常数相媲美。观察到的相对特异性和周转率之间的趋势可以表示为负相关因子和正相关因子的乘积。这提供了一个简单的动力学方面的相对特异性的自然变化，以及所获得的定点诱变结果的解释。我们证明，动力学行为显示出较小的，而不是更多的限制RuBisCO，符合越来越多的经验证据，相对特异性的更高的变异性。总之，我们的分析支持解释的起源之间的权衡特异性和营业额，由于蛋白质的稳定性和活性之间的竞争，而不是限制之间的速率常数所施加的基础化学。我们的分析表明，同时提高特异性和周转率的RuBisCO是可能的。
The ubiquitous enzyme Ribulose 1,5-bisphosphate carboxylase-oxygenase (RuBisCO) fixes atmospheric carbon dioxide within the Calvin-Benson cycle that is utilized by most photosynthetic organisms. Despite this central role, RuBisCO's efficiency surprisingly struggles, with both a very slow turnover rate to products and also impaired substrate specificity, features that have long been an enigma as it would be assumed that its efficiency was under strong evolutionary pressure. RuBisCO's substrate specificity is compromised as it catalyzes a side-fixation reaction with atmospheric oxygen; empirical kinetic results show a trend to tradeoff between relative specificity and low catalytic turnover rate. Although the dominant hypothesis has been that the active-site chemistry constrains the enzyme's evolution, a more recent study on RuBisCO stability and adaptability has implicated competing selection pressures. Elucidating these constraints is crucial for directing future research on improving photosynthesis, as the current literature casts doubt on the potential effectiveness of site-directed mutagenesis to improve RuBisCO's efficiency. Here we use regression analysis to quantify the relationships between kinetic parameters obtained from empirical data sets spanning a wide evolutionary range of RuBisCOs. Most significantly we found that the rate constant for dissociation of CO2 from the enzyme complex was much higher than previous estimates and comparable with the corresponding catalytic rate constant. Observed trends between relative specificity and turnover rate can be expressed as the product of negative and positive correlation factors. This provides an explanation in simple kinetic terms of both the natural variation of relative specificity as well as that obtained by reported site-directed mutagenesis results. We demonstrate that the kinetic behaviour shows a lesser rather than more constrained RuBisCO, consistent with growing empirical evidence of higher variability in relative specificity. In summary our analysis supports an explanation for the origin of the tradeoff between specificity and turnover as due to competition between protein stability and activity, rather than constraints between rate constants imposed by the underlying chemistry. Our analysis suggests that simultaneous improvement in both specificity and turnover rate of RuBisCO is possible.
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