Westfall David A, Krishnamoorthy Ganesh, Wolloscheck David, Sarkar Rupa, Zgurskaya Helen I, Rybenkov Valentin V
Department of Chemistry and Biochemistry, University of Oklahoma, Stephenson Parkway, Norman, OK, United States of America.
PLoS One. 2017 Sep 19;12(9):e0184671. doi: 10.1371/journal.pone.0184671. eCollection 2017.
Cell envelopes of many bacteria consist of two membranes studded with efflux transporters. Such organization protects bacteria from the environment and gives rise to multidrug resistance. We report a kinetic model that accurately describes the permeation properties of this system. The model predicts complex non-linear patterns of drug uptake complete with a bifurcation, which recapitulate the known experimental anomalies. We introduce two kinetic parameters, the efflux and barrier constants, which replace those of Michaelis and Menten for trans-envelope transport. Both compound permeation and efflux display transitions, which delineate regimes of efficient and inefficient efflux. The first transition is related to saturation of the transporter by the compound and the second one behaves as a bifurcation and involves saturation of the outer membrane barrier. The bifurcation was experimentally observed in live bacteria. We further found that active efflux of a drug can be orders of magnitude faster than its diffusion into a cell and that the efficacy of a drug depends both on its transport properties and therapeutic potency. This analysis reveals novel physical principles in the behavior of the cellular envelope, creates a framework for quantification of small molecule permeation into bacteria, and should invigorate structure-activity studies of novel antibiotics.
许多细菌的细胞包膜由两层布满外排转运蛋白的膜组成。这种结构保护细菌免受外界环境影响，并导致多药耐药性。我们报告了一个动力学模型，该模型准确描述了该系统的渗透特性。该模型预测了药物摄取的复杂非线性模式，并伴有分岔现象，这重现了已知的实验异常情况。我们引入了两个动力学参数，即外排常数和屏障常数，以取代米氏动力学参数用于跨包膜运输。化合物的渗透和外排均显示出转变，这划分了高效和低效外排的区域。第一个转变与化合物使转运蛋白饱和有关，第二个转变表现为分岔，涉及外膜屏障的饱和。这种分岔现象在活细菌中通过实验观察到。我们还发现，药物的主动外排速度可能比其扩散进入细胞的速度快几个数量级，并且药物的疗效既取决于其转运特性，也取决于其治疗效力。该分析揭示了细胞包膜行为中的新物理原理，创建了一个量化小分子渗透进入细菌的框架，并应能推动新型抗生素的构效关系研究。
