Reconstructed Ancestral Enzymes Impose a Fitness Cost upon Modern Bacteria Despite Exhibiting Favourable Biochemical Properties
Reconstructed Ancestral Enzymes Impose a Fitness Cost upon Modern Bacteria Despite Exhibiting Favourable Biochemical Properties
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DOI：
10.1007/s00239-015-9697-5
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发表时间：
2015-10-01
影响因子：
3.9
通讯作者：
Arcus, Vickery L.
中科院分区：
文献类型：
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作者：
Hobbs, Joanne K.;Prentice, Erica J.;Arcus, Vickery L.
祖先序列重建已被广泛用于研究历史酶的进化，无论是从生物化学和细胞的角度。与同时代的蛋白质/酶相比，重建的祖先蛋白质/酶的两个性质通常是明确的-高热稳定性和高催化活性。增加的蛋白质稳定性与较低的聚集速率、较高的可溶性蛋白质丰度和更大的进化能力相关，因此，这些蛋白质可以被认为比它们的当代对应物“上级”。在这项研究中，我们调查的有利的体外生化特性重建的祖先酶和它们赋予在体内的生物体健身之间的关系。我们以前已经重建了几个祖先的酶LeuB，这是必不可少的亮氨酸生物合成。我们最初的适应性实验表明，ANC 4（一种表现出高稳定性和活性的重建LeuB）的过表达只能部分拯救Delta leuB菌株的生长，并且补充了这种酶的菌株被携带其后代之一的菌株所击败。当我们扩大我们的研究，包括五个重建的LeuBs和一个当代，我们发现，无论是在体外蛋白质的稳定性，也没有催化率与健身。相反，健身表现出很强的，负相关的估计进化年龄（基于系统发育关系）。我们的研究结果表明，对于重建的祖先酶，体外上级特性并不转化为体内的生物体适应性。健身和推断年龄的祖先LeuB酶之间的关系的分子基础是未知的，但可能与重建过程。我们还假设，祖先的酶可能是不兼容的其他当代酶的代谢网络。
Ancestral sequence reconstruction has been widely used to study historical enzyme evolution, both from biochemical and cellular perspectives. Two properties of reconstructed ancestral proteins/enzymes are commonly reported-high thermostability and high catalytic activity-compared with their contemporaries. Increased protein stability is associated with lower aggregation rates, higher soluble protein abundance and a greater capacity to evolve, and therefore, these proteins could be considered "superior" to their contemporary counterparts. In this study, we investigate the relationship between the favourable in vitro biochemical properties of reconstructed ancestral enzymes and the organismal fitness they confer in vivo. We have previously reconstructed several ancestors of the enzyme LeuB, which is essential for leucine biosynthesis. Our initial fitness experiments revealed that overexpression of ANC4, a reconstructed LeuB that exhibits high stability and activity, was only able to partially rescue the growth of a Delta leuB strain, and that a strain complemented with this enzyme was outcompeted by strains carrying one of its descendants. When we expanded our study to include five reconstructed LeuBs and one contemporary, we found that neither in vitro protein stability nor the catalytic rate was correlated with fitness. Instead, fitness showed a strong, negative correlation with estimated evolutionary age (based on phylogenetic relationships). Our findings suggest that, for reconstructed ancestral enzymes, superior in vitro properties do not translate into organismal fitness in vivo. The molecular basis of the relationship between fitness and the inferred age of ancestral LeuB enzymes is unknown, but may be related to the reconstruction process. We also hypothesise that the ancestral enzymes may be incompatible with the other, contemporary enzymes of the metabolic network.