Microbial siderophore-specific innate immune responses

性状（由申请方提供）：Siderocalin（脂质运载蛋白2），发现于中性粒细胞颗粒、子宫分泌物中，由上皮细胞分泌，对炎症或肿瘤发生有反应。也是一种急性期蛋白，在细菌感染期间血清和滑膜中的水平显著升高。虽然涉及不同的生理过程，铁载体蛋白的功能是神秘的，直到我们最近鉴定出这种蛋白质的特异性，高亲和力配体：细菌酚酸盐型铁载体，如肠螯合素（又名肠杆菌素; KD = 0.4纳摩尔）和混合型羧基分枝杆菌素铁载体。因此，我们建议，铁黄素功能作为抗菌剂，螯合铁载体复合物，补充一般的抗微生物铁耗竭策略的先天免疫系统。支持这一假设，我们已经发现，siderocalin是一种有效的抑菌剂在体外铁限制条件下，当敲除，使动物非常容易受到细菌感染。Siderocalin显然使用一种新的简并识别机制与不同类型的铁载体交叉反应，从而拓宽了响应的实用性。这一功能假说也合理化了一些铁载体与毒力的关联：通过交替利用铁载体与铁运载蛋白的亲和力显着降低，病原体可以逃脱铁运载蛋白介导的铁剥夺。本项目的目标是确定先天免疫反应的铁载体特异性组分如何识别微生物铁载体。 在目标1中，我们建议继续对铁载体进行晶体学、诱变和生物物理学研究，以及一组天然、合成和设计的铁载体，以充分描述这种蛋白质如何识别铁载体。Siderocalin是多种脂质运载蛋白家族的成员。 我们还确定了四个远亲相关的小鼠和鸟类的脂质运载蛋白，无论是明显结合细菌铁载体的替代光谱或预测的基础上建模研究。在目标2中，我们提出了类似的结构和生物化学研究这些蛋白质类似地解析其识别机制。 最终，这些研究不仅将充分表征抗菌免疫监视的这一组成部分，而且还将允许继续和未来的毒力和发病机制研究-以及定义这些蛋白质作为新型抗菌治疗剂的潜在用途。

DESCRIPTION (provided by applicant): Siderocalin (lipocalin 2), found in neutrophil granules, uterine secretions and secreted from epithelial cells in response to inflammation or tumorigenesis. is also an acute phase protein, with markedly elevated levels in the serum and the synovium during bacterial infection. Though implicated in diverse physiological processes, siderocalin's function was mysterious until our recent identification of specific, high-affinity ligands for this protein: bacterial phenolate-type ferric siderophores, such as enterochelin (aka enterobactin; KD = 0.4 nanomolar) and the mixed-type carboxymycobactin ferric siderophores. We therefore propose that siderocalin functions as an antibacterial agent, sequestering iron as ferric siderophore complexes, complementing the general anti-microbial iron-depletion strategy of the innate immune system. Supporting this hypothesis, we have found that siderocalin is a potent bacteriostatic agent in vitro under iron-limiting conditions and, when knocked-out, renders animals remarkably susceptible to bacterial infection. Siderocalin apparently uses a novel, degenerate recognition mechanism to cross-react with distinct types of siderophores, broadening the utility of the response. This functional hypothesis also rationalizes the association of some siderophores with virulence: by alternately utilizing siderophores with markedly reduced affinity for siderocalin, pathogens can escape siderocalin-mediated iron-deprivation. The goal of this project is to determine how siderophore-specific components of the innate immune response recognize microbial siderophores. In Aim 1, we propose continuing crystallographic, mutagenesis and biophysical studies of siderocalin, and a panel of natural, synthetic and designed siderophores, to fully delineate how this protein recognizes siderophores. Siderocalin is a member of the diverse lipocalin protein family. We have also identified four distantly-related murine and avian lipocalins that either demonstrably bind alternate spectrums of bacterial siderophores or are predicted to on the basis of modeling studies. In Aim 2, we propose analogous structural and biochemical studies of these proteins to similarly parse their recognition machinery. Ultimately, these studies will not only fully characterize this component of antibacterial immune surveillance, but will also allow continuing and future studies of virulence and pathogenesis - as well as defining the potential utility of these proteins as novel anti-bacterial therapeutics.