BIO-ORGANIC MECHANISMS OF PEPTIDE ANTIBIOTICS

细菌对抗生素的耐药性严重限制了我们战胜传染病的能力。在几乎所有医院获得性病原体-抗菌素组合中都出现了耐药性病例。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更好的抗耐药表型活性的替代抗生素。Ramoplanin是一种新型的β -薄片脂肪沉积肽抗生素，具有抗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这三种重要的革兰氏阳性机会性人类病原体的活性。Ramoplanin似乎在MurG水平上阻止细菌细胞壁的发育，其机制尚不清楚，MurG是一种糖基转移酶，参与肽聚糖生物合成的中间阶段。由于MurG活性对细菌细胞壁发育至关重要，因此它是抗菌设计的一个有吸引力的靶点。利用Ramoplanin的临床抗生素潜力关键取决于获得对其结构的合成途径并解开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，以完全将结构与抗生素功能联系起来。我们计划采用固相方法合成Ramoplanin及相关类似物，从而提供一种有利于调节其理化性质的通用合成途径。我们计划确定Ramoplanin的分子靶点，并确定相互作用能、特异性和抑制复合物的结构。我们将评估Ramoplanin对MurG反应的抑制作用，以及对发生在细菌细胞膜外表面的机制相关的肽聚糖转糖基化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一个清晰的图景，并促进新一代抗生素的设计、合成和生物学评价，这些抗生素能够对抗细菌对抗生素的耐药性。

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.