Biochemistry of Bacterial Cell Membranes

描述（由申请人提供）：致病菌中多重耐药的日益流行是对人类健康的主要威胁。特别是革兰氏阴性菌通常对许多抗菌剂具有内在耐药性，并且这种内在耐药性很容易因常见突变而增加。近年来，我们和其他实验室的研究得出结论，这种耐药性通常是由阻止药物进入细菌细胞内的靶细胞的机制介导的。两个“障碍”以真正协同的方式发挥作用。首先，革兰氏阴性外膜极大地阻碍了亲水和亲脂抗菌剂的进入，因为孔蛋白通道的狭窄或缺乏使得亲水抗菌剂难以进入，并且因为该膜的脂多糖-磷脂不对称双分子层大大减缓了亲脂抗菌剂的进入。其次，一些成功穿过外膜的抗生素分子被无处不在的多药外排泵主动泵出，这些泵通常显示出令人难以置信的广泛底物特异性。在临床来源的多重耐药菌株中，这些泵经常过量生产；这种机制特别麻烦，因为使用一种药物可能同时导致对大多数现有抗生素产生耐药性。我们将继续研究这两个阶段的防范准入机制。在外膜通透性方面，我们将研究一些孔被折叠而只产生少数开放通道的机制。我们还将研究使脂多糖-磷脂双分子层如此异常不渗透的分子机制，并将首次测量氨基糖苷穿过外膜的进入。在多药外排泵领域，我们将继续研究大肠杆菌的主要多药外排泵AcrAB-TolC的结构和功能，以了解为什么这种转运体可以处理如此广泛的化合物。这些研究结果对今后合成和半合成抗菌化合物的开发具有重要的指导意义。

DESCRIPTION (provided by applicant): The increasing prevalence of multiple drug resistance in pathogenic bacteria is a major threat to human health. Especially Gram-negative bacteria are often intrinsically resistant to a number of antimicrobial agents, and such intrinsic resistance may easily become increased by common mutations. Studies in our and other laboratories in recent years led to the conclusion that such resistance is frequently mediated by mechanisms preventing the access of agents to their targets inside bacterial cells. Two "barriers" work in a truly synergistic manner. First, the Gram-negative outer membrane greatly retards the entry of antimicrobial agents, both hydrophilic and lipophilic, because the narrowness or paucity of porin channels makes the entry of hydrophilic agents difficult, and because the lipopolysaccharide-phospholipid asymmetric bilayer of this membrane slows down drastically the entry of lipophilic agents. Second, a few molecules of antibiotics that succeed in crossing the outer membrane are actively pumped out by ubiquitous multidrug efflux pumps that often show an incredibly wide substrate specificity. The pumps are frequently overproduced in the multidrug- resistant strains from clinical sources; this mechanism is especially troublesome because the use of a single drug can lead to simultaneous resistance to most of the existing antibiotics. We will continue to study both phases of the access-prevention mechanism. In the area of outer membrane permeability, we will study the mechanism whereby some porins are folded to produce only a few open channels. We will also study the molecular mechanism which makes the lipopolysaccharide-phospholipid bilayer so exceptionally impermeable, and will measure, for the first time, the entry of aminoglycosides across the outer membrane. In the area of multidrug efflux pumps, we will continue our studies of the structure and function of the major multidrug efflux pump of Escherichia coli, AcrAB-TolC, to understand why this transporter can handle such a wide range of compounds. The results of these studies will be very useful for the development of synthetic and semisynthetic antimicrobial compounds in the future.