Synthesis and function of Queuosine in Bacteria

肌苷（Q）是唯一可以挽救的tRNA修饰，将营养与翻译联系起来。 在真核生物中，补救是唯一的Q合成途径，并提供了前体碱基精氨酸（q 通过饮食或肠道微生物菌群，并直接插入到目标tRNA中。大约50%的肠道 微生物群模型物种被预测为营养缺陷型，并且必须挽救Q前体。在 一般来说，细菌Q补救酶的特性非常差，特别是在革兰氏阳性菌中， 肠道和口腔微生物组中普遍存在的细菌。这个项目的重点是发现 以及表征Q补救酶以及新的Q合成酶和Q降解酶， 与人类宿主相关的细菌中。我们还将详细探讨 Q在口腔主要致病菌变形链球菌中的初步研究结果提示了Q的作用 和/或Q前体在生物膜形成、感受态和毒力中的作用。目标1的目标是 实验表征了预测挽救Q前体的两个主要转运蛋白家族： YhhQ/COG 1738家族和能量偶联因子（ECF）底物特异性家族 (QueT/QtrT）。事实上，这些家庭不是等功能的，成员似乎是分歧的， 取决于种类，取决于运输不同Q前体的能力。目标2侧重于 催化最后一步的新型Q合成酶QueH的生物化学表征 通过一个前所未有的反应进行生物合成。在目标1和2中，我们还将寻找 Q代谢中的“缺失”组分，例如普遍肠道微生物组中缺失的转运蛋白 细菌如短杆菌属和潜在的Q催化剂基因。最后的目的将探讨 Q合成基因在S.变异体测试假设，他们可能有重要的作用， 监管权限。这项拟议的研究意义重大，因为微生物群是一种 是甜菜碱微量营养素的关键来源，因此充分表征了细菌Q合成， 在人类相关细菌中的补救和降解途径是充分 了解并模拟这一关键资源的竞争动态。此外，由于 S的重要性。牙齿龋齿发展中的变异，了解的分子基础， 观察到的Q合成基因在能力中的重要性将增加我们对关键的理解。 这种生物如何在其口腔微生物生态位中与其他生物竞争的组成部分。

Queuosine (Q) is the only tRNA modification that can be salvaged, linking nutrition to translation. In eukaryotes salvage is the only Q synthesis route and the precursor base queuine (q) is provided by the diet or the gut microflora and directly inserted in target tRNAs. Around 50% of the gut microbiota model species are predicted to be auxotrophs and must salvage a Q precursor. In general, bacterial Q salvage enzymes are very poorly characterized, particularly in Gram-positive bacteria that are prevalent in the gut and oral microbiome. This project focuses on discovering and characterizing Q salvage enzymes as well as novel Q synthesis and Q degradation enzymes in bacteria associated with the human host. We will also explore in detail the physiological role of Q in the major oral pathogen Streptococcus mutans as preliminary results suggest a role of Q and/or Q precursors in biofilm formation, competence and virulence. The goal of Aim 1 is to experimentally characterize two main families of transporters predicted to salvage Q precursors: the YhhQ/COG1738 family and the Energy-Coupling Factor (ECF) substrate specificity families (QueT/QtrT). Indeed, these families are not iso-functional, and members seem to diverge, depending on the species, on the ability to transport different Q precursors. Aim 2 focuses on the biochemical characterization of the novel Q synthesis enzyme QueH that catalyzes the last step of biosynthesis through an unprecedented reaction. In both Aims 1 and 2, we will also hunt for “missing” components in Q metabolism such as missing transporters in prevalent gut microbiome bacteria such as Brevibacteria and potential Q catabolism genes. The final aim will explore the role of Q synthesis genes in S. mutans testing the hypothesis that they could have important roles in regulation of competence. The proposed research is significant because the microbiota is a key source for the queuine micronutrient, hence fully characterizing the bacterial Q synthesis, salvage and degradation pathways in human associated bacteria is a requirement to fully understand and model the competition dynamics for this key resource. In addition, because of the importance of S. mutans in dental caries progression, understanding the molecular basis for the observed importance of Q synthesis genes in competence will increase our understanding of key component of how this organism competes with others in its oral microbiome niche.