Acquisti Claudia, Kumar Sudhir, Elser James J
Biodesign Institute, Center for Evolutionary Functional Genomics, Arizona State University, Tempe, AZ 85287-5301, USA.
Proc Biol Sci. 2009 Jul 22;276(1667):2605-10. doi: 10.1098/rspb.2008.1960. Epub 2009 Apr 15.
Nitrogen (N) is a fundamental component of nucleotides and amino acids and is often a limiting nutrient in natural ecosystems. Thus, study of the N content of biomolecules may establish important connections between ecology and genomics. However, while significant differences in the elemental composition of whole organisms are well documented, how the flux of nutrients in the cell has shaped the evolution of different cellular processes remains poorly understood. By examining the elemental composition of major functional classes of proteins in four multicellular eukaryotic model organisms, we find that the catabolic machinery shows substantially lower N content than the anabolic machinery and the rest of the proteome. This pattern suggests that ecological selection for N conservation specifically targets cellular components that are highly expressed in response to nutrient limitation. We propose that the RNA component of the anabolic machineries is the mechanistic force driving the elemental imbalance we found, and that RNA functions as an intracellular nutrient reservoir that is degraded and recycled during starvation periods. A comparison of the elemental composition of the anabolic and catabolic machineries in species that have experienced different levels of N limitation in their evolutionary history (animals versus plants) suggests that selection for N conservation has preferentially targeted the catabolic machineries of plants, resulting in a lower N content of the proteins involved in their catabolic processes. These findings link the composition of major cellular components to the environmental factors that trigger the activation of those components, suggesting that resource availability has constrained the atomic composition and the molecular architecture of the biotic processes that enable cells to respond to reduced nutrient availability.
氮（N）是核苷酸和氨基酸的基本组成成分，并且在自然生态系统中常常是一种限制性营养素。因此，对生物分子中氮含量的研究可能会在生态学和基因组学之间建立重要联系。然而，尽管全生物体元素组成的显著差异已有充分记录，但细胞内营养物质的流动如何塑造了不同细胞过程的进化仍知之甚少。通过研究四种多细胞真核模式生物中主要功能类别的蛋白质的元素组成，我们发现分解代谢机制的氮含量显著低于合成代谢机制和蛋白质组的其他部分。这种模式表明，对氮保存的生态选择特别针对那些在营养限制下高表达的细胞成分。我们提出，合成代谢机制的RNA成分是驱动我们所发现的元素失衡的机制力量，并且RNA作为一种细胞内营养库，在饥饿期间会被降解和再循环。对在进化历史中经历了不同程度氮限制的物种（动物与植物）的合成代谢和分解代谢机制的元素组成进行比较表明，对氮保存的选择优先针对植物的分解代谢机制，导致参与其分解代谢过程的蛋白质的氮含量较低。这些发现将主要细胞成分的组成与触发这些成分激活的环境因素联系起来，表明资源可用性限制了使细胞能够应对营养可用性降低的生物过程的原子组成和分子结构。
