BIO-ORGANIC MECHANISMS OF PEPTIDE ANTIBIOTICS

细菌对抗生素的抗药性严重限制了我们战胜传染病的能力。 耐药病例几乎出现在所有医院获得性病原体-抗菌药物组合中。 很快，我们最严重的传染病威胁将无法治愈，因为我们的有效抗生素库正在减少。 我们的长期研究目标是开发生物学上有趣的肽抗生素的合成途径，深入了解其作用机制/模式，并将所获得的知识应用于开发具有改善耐药表型活性的替代抗生素。 该提案描述了Ramoplanin的全合成和机理表征，Ramoplanin是一种新型β折叠脂缩肽抗生素，具有针对耐甲氧西林金黄色葡萄球菌、耐万古霉素屎肠球菌和耐头孢菌素肺炎链球菌（三种重要的革兰氏阳性机会性人类病原体）的活性。 通过一种不清楚的机制，雷莫拉宁似乎在MurG水平上阻止细菌细胞壁发育，MurG是一种参与肽聚糖生物合成中间阶段的糖基转移酶。 由于MurG活性对于适当的细菌细胞壁发育是必不可少的，因此它是抗菌设计的有吸引力的目标。 利用雷莫拉宁的临床抗生素潜力关键在于获得对其结构的合成访问并解卷积其作用机制的最亲密细节。 为了实现这一目标，我们将协同合并全合成，机械酶学和蛋白质生物物理学，以完全关联结构与抗生素功能。 我们计划使用固相方法合成雷莫拉宁和相关类似物，从而提供一个通用的合成路线，以有利地调节其理化性质。 我们计划确定雷莫拉宁的分子靶点，并确定抑制复合物的相互作用能，特异性和结构。 我们将评估雷莫拉宁对MurG反应和发生在细菌细胞膜外表面的机械相关肽聚糖转糖基交联反应的抑制作用。 总的来说，这些研究将为Ramoplanin抑制肽聚糖生物合成的机制提供清晰的图像，并促进能够对抗细菌对抗生素耐药性的新一代抗生素的设计，合成和生物学评价。

Bacterial resistance to antibiotics has seriously limited our capacity to overcome infectious disease. Cases of resistance have emerged in virtually all hospital-acquired pathogen-antimicrobial combinations. Soon our most serious infectious threats will be untreatable given our dwindling arsenal of effective antibiotics. Our long-term research goals are to develop synthetic access to biologically interesting peptide antibiotics, to gain insight into their mechanism/mode of action, and to apply the knowledge gained to the development of alternative antibiotics with improved activity against resistant phenotypes. This proposal describes the total synthesis and mechanistic characterization of Ramoplanin, a novel beta-sheet lipodepsipeptide antibiotic with proven activity against methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecium, and cephalosporin-resistant Streptococcus pneumonia, three important Gram positive opportunistic human pathogens. By an unclear mechanism, Ramoplanin appears to arrest bacterial cell wall development at the level of MurG, a glycosyltransferase involved in an intermediate stage of peptidoglycan biosynthesis. Since MurG activity is essential for proper bacterial cell wall development, it is an attractive target for antibacterial design. Harnessing the clinical antibiotic potential of Ramoplanin critically hinges on gaining synthetic access to its structure and deconvoluting the most intimate details of its mechanism of action. To accomplish this we will synergistically merge total synthesis, mechanistic enzymology and protein biophysics to completely correlate structure to antibiotic function. We plan to synthesize Ramoplanin and related analogues using solid-phase methods, thus providing a general synthetic route to favorably modulate its physiochemical properties. We plan to identify the molecular target of Ramoplanin and determine the interaction energies, specificities, and structure of the inhibitory complex. We will assess the inhibitory effect of Ramoplanin on the MurG reaction and on the mechanistically related peptidoglycan transglycosylation cross-linking reaction that takes place on the outer surface of the bacterial cell membrane. Collectively these studies will provide a clear picture of the mechanism of Ramoplanin inhibition of peptidoglycan biosynthesis and promote the design, synthesis, and biological evaluation of a new generation of antibiotics capable of combating bacterial resistance to antibiotics.