SGER: Novel Nitrogenase-like Proteins and the Evolution of the Nitrogen Cycle

这个SGER项目涉及一类可能在进化上与固氮酶相关的新型酶的特征。这些蛋白质是用基因组方法在许多生物体中发现的，其中包括几个非重氮营养的生物体。这些蛋白质在进化上与固氮酶有关，但几乎可以肯定催化其他未知的化学反应。这些蛋白质可能是固氮酶原始祖先的直系后代，因为它们在系统发育树中的基础位置和复合体的还原酶部分的单一亚基类型。在这个项目中，这些固氮酶样蛋白(NflH和Nfld)的基因将从詹纳斯基甲烷球菌中克隆出来，并将在大肠杆菌中表达。使用从这些重组蛋白中获得的抗体，将提纯和鉴定来自詹纳斯基分枝杆菌的这些相同蛋白的天然形式。有可能确定这些蛋白质的独特活性，这可能意味着在早期地球上有一个前固氮酶同系物的作用。如果在这些同源物中发现类似的底物或活性，也可能进一步了解固氮酶的机制。广泛的影响：这个项目将加强我们对氮循环起源和进化的理解，这将为生命的早期进化和新陈代谢的起源提供重要的见解。该项目将涉及一名博士后研究员的培训，并将有助于发展一支经过科学培训的劳动力队伍。

This SGER project is concerned with the characterization of a putative new class of enzymes evolutionarily related to nitrogenase. These proteins have been discovered using genomic methods in a number of organisms, including several that are not diazotrophic. The proteins are evolutionarily related to nitrogenase but almost certainly catalyze other, as yet unknown, chemical reactions. These proteins may be the direct descendents of the primitive ancestors of nitrogenase, because of their basal position in the phylogenetic tree and the single type of subunit in the reductase portion of the complex. In this project, genes for these nitrogenase-like proteins (NflH and NflD) will be cloned from Methanococcus jannaschii and will be expressed in E. coli. Using antibodies obtained from these recombinant proteins, native forms of these same proteins from M. jannaschii will be purified and characterized. It is possible that a unique activity will be determined for these proteins, which could imply a role for a pre-nitrogenase homolog on the early Earth. A further understanding of the mechanism of nitrogenase might also be realized, if a similar substrate or activity is found in these homologs.Broader Impacts: This project will enhance our understanding of the origin and evolution of the nitrogen cycle, which will give important insights into the early evolution of life and the origin of metabolism. This project will involve training of a postdoctoral fellow and will contribute to the development of a scientifically trained workforce.