Molecular Characterization of New Bacterial Factors in Phospholipid Transport and Genome Integrity

尽管大肠杆菌是研究得最好的微生物之一，也是开发抗菌剂的主力，但只有69%的大肠杆菌基因被赋予了功能，而31%（4,247个中的1,336个）没有实验数据。这些未表征的（定义不明确或孤儿）基因的生物学作用可以根据它们与注释的基因产物的关联来预测，通过我们生成的大规模蛋白质或遗传相互作用网络的所谓“关联内疚”原理。然而，这些研究补充，而不是取代直接的机制调查的需要。在这个研究计划中，我提出了两个目标，这是建立在我的长期研究计划和坚实的初步数据。本课题的长期目标是：（1）研究孤儿基因在大肠杆菌中的生物学作用;从我们的相互作用图中发现与保守过程相关的大肠杆菌;（2）推进我们对可能对耐药细菌产生影响的重要细菌机制的理解。为了实现这些目标，我以前的NSERC发现基金揭示了一些E。coli孤儿基因功能预测。更具体地说，我首次提出了理解3个孤儿E.大肠杆菌基因和广泛研究的磷脂运输和基因组完整性的过程，我们在以前的相互作用筛选确定。我们发现与这些特定过程相关的孤儿现在正在研究界受到越来越多的关注，因此我优先考虑这3个孤儿候选人进行详细的机械表征。越来越多的证据表明脂多糖是如何合成、运输和插入外膜的，但磷脂通过辅助蛋白在细菌内外膜之间运输的机制尚不清楚。同时，新兴的研究表明，聚合酶PHP（聚合酶和组氨醇磷酸酶）结构域能够协调染色体复制过程中的校对和聚合酶活性。因此，我利用与PHP结构域具有高度序列相似性的孤儿蛋白的结构来理解其作为基因组完整性中的核酸酶的作用。因此，我假设两个目标孤儿参与维持外膜脂质不对称性，第三个孤儿在基因组完整性过程中起校对核酸酶的作用。我将使用生物化学，遗传学，结构和分子方法来测试这些假设，我预计这些方法将提供革兰氏阴性细菌如何在磷脂运输和基因组完整性的复杂细菌过程中组织目标孤儿的新知识，并为研究微生物生理学的研究人员提供有价值的机制见解。

Despite being one of the best-studied microbes and a workhorse for the development of antimicrobials, only 69% of Escherichia coli genes have been assigned function, while 31% (1,336 of 4,247) have no experimental data. The biological roles of these uncharacterized (ill-defined or orphan) genes can be predicted based on their association with annotated gene products through the so-called “guilt-by-association” principle from large-scale protein or genetic interaction networks we have generated. However, such studies complement rather than replace the need for direct mechanistic investigations. In this research program, I propose two objectives that are built on my long-term research program and solid preliminary data. The long-term goals of my bacterial research program are to: (1) characterize the biological roles of orphan genes in E. coli that are connected with conserved processes from our interaction maps; and (2) advance our understanding of vital bacterial machineries that could have consequences to drug-resistant bacteria. Towards achieving these goals, my previous NSERC discovery grant revealed mechanisms for some of the E. coli orphan gene function predictions. More specifically, I propose for the first time, methods to understand the biological significance of connections between 3 orphan E. coli genes and the widely-studied phospholipid trafficking and genome integrity processes that we identified in previous interaction screens. Orphans we found to associate with these particular processes are now receiving increased attention in the research community, and as such I have prioritized these 3 orphan candidates for detailed mechanistic characterization.******Accumulating and still evolving evidence has shown how lipopolysaccharide is synthesized, trafficked and inserted into the outer membrane, yet the mechanisms by which phospholipids are transported via auxiliary proteins between the bacterial inner and outer membrane is not known. As well, emerging studies suggest that the polymerase PHP (Polymerase and Histidinol Phosphatase) domain enables coordination of proofreading and polymerase activities during chromosomal replication. I thus exploited the structure of an orphan protein that has high sequence similarity to the PHP domain to understand its role as a nuclease in genome integrity. Therefore, I hypothesize that two target orphans are involved in the maintenance of outer membrane lipid asymmetry, and a third orphan to function as a proofreading nuclease in the genome integrity process. I will test these hypotheses using biochemical, genetic, structural and molecular approaches, which I anticipate will provide new knowledge of how a Gram-negative bacteria organizes targeted orphans in the intricate bacterial processes of phospholipid trafficking and genome integrity, and generate valuable mechanistic insights for researchers studying the physiology of microbes.**