Synthesis of New Ligands for the Characterization of Siderophore-ExFABP Interacti

摘要 癌症和癌症治疗通常伴随着免疫系统的严重削弱。 细菌是中性粒细胞减少的癌症患者的大多数外来感染的罪魁祸首 这是一个重大的健康风险。初步研究表明，人类铁黄素是Lipocalin的一员 结合蛋白家族，通过与微生物铁载体结合，抑制细菌生长 铁的封存。鉴于哺乳动物的铁水平会因病原体和肿瘤的生长而下降， 通过铁微生物铁载体复合体靶向结合铁可能是一种有用的治疗策略。 癌症和细菌感染。我们发现，Ex-FABP是一种相关的Lipocalin蛋白，在 鸡胚发育，也结合了不同结构类别的铁铁载体复合体。我们的目标是 用化学方法合成天然存在的和设计的细菌铁载体类似物，以实现 全面了解铁载体特有的先天免疫系统的相互作用。为了努力解析 铁黄素和Ex-FABP的识别模式，我们将制备绿球蛋白的氧代和亚甲基变体，a 假单胞菌含铁载体能与Ex-FABP结合，但不能与铁蛋白结合。具体的假设是 褐素硫唑啉环上的硫原子由于与铁黄素发生空间碰撞而与铁黄素结合。 花萼中的结合水分子。用恶唑啉环取代噻唑啉可能会模仿 其他高亲和力铁蛋白的结合方式，如羧基粘菌杆菌素。因为自然发生的 绿球蛋白也是一种不稳定的非对映异构体混合物，我们建议以构型合成。 稳定的基于Pro的类似物，以确定Ex-FABP的离散立体化学要求 有约束力的。我们还将进行第一次化学合成(第I组)，这是一种结合在一起的复杂多肽 特别是对前FABP。全化学合成的优点包括能够追求合成 类似物和难以从细菌来源获得的同质配体的分离。一次 如果这些侧基团的合成纯样本可用，我们将继续进行定量结合研究， 体外生长停滞试验和x射线结晶学。这项研究的结果将有助于 鉴定其他蛋白质特异的微生物铁载体，为蛋白质突变研究奠定基础 微生物选择性抗生素治疗的手段。

ABSTRACT Cancer and cancer therapy are commonly accompanied by a severe weakening of the immune system. Bacteria are responsible for the majority of adventitious infections in neutropenic cancer patients and thus pose a significant health risk. Preliminary studies have shown that human siderocalin, a member of the lipocalin family of binding proteins, binds to microbial ferric siderophores and inhibits bacetrial growth through the sequestration of iron. Given that mamalian iron levels drop in response to pathogens and tumor growth, targeted binding of iron via ferric microbial siderophore complexes may be a useful strategy in the treatment of cancer and bacterial infections. We have found that Ex-FABP, a related lipocalin protein expessed during chicken embryo development, also binds ferric siderophore complexes of distinct structural classes. Our aim is to chemically synthesize naturally occurring and designed analogs of bacterial siderophores in order to achieve a complete understanding of siderophore-specific innate immune system interactions. In an effort to parse the recognition modes of siderocalin and Ex-FABP, we will prepare oxo and methylene variants of pyochelin, a Pseudomonas siderophore that binds to Ex-FABP, but not to siderochelin. The specific hypothesis is that the sulfur atom in the thiozoline ring of pyochelin preculdes binding to siderocalin due to a steric clash with a tightly bound water molecule in the calyx. Replacement of a thiazoline with an oxazoline ring will potentially mimic the binding mode of other high-affinity siderocalins such as the carboxymycobactins. Because naturally occuring pyochelin also exists as an unstable mixture of diastereomers, we propose to synthesize configurationally stable proline-based analogs in order to determine the discrete stereochemical requirements of Ex-FABP binding. We will also undertake the first chemical synthesis of (group I) pyoverdin, a complex peptide that binds specifically to Ex-FABP. The advantages of total chemical synthesis include the ability to pursue synthetic analogs and the isolation of homogenous ligand that is difficult to obtain from bacterial sources. Once synthetically pure samples of these sideophores are available, we will proceed with quanitative binding studies, in vitro growth arrest assays, and x-ray crystallography. Results emanating from this research will aid in the identification of other protein-specific microbial siderophores and lay the foundation for protein mutation as a means toward microbe-selective antibiotic therapy.