Permeation rates of penicillins indicate that Escherichia coli porins function principally as nonspecific channels
Permeation rates of penicillins indicate that Escherichia coli porins function principally as nonspecific channels
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DOI：
10.1073/pnas.1310333110
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发表时间：
2013-07-09
影响因子：
11.1
通讯作者：
Nikaido, Hiroshi
中科院分区：
文献类型：
--
作者：
Kojima, Seiji;Nikaido, Hiroshi
β-内酰胺等小的亲水性化合物通过孔蛋白通道扩散穿过革兰氏阴性细菌的外膜，这些通道最初被认为是没有任何特异性的非特异性通道。然而，自从2002年在OmpF通道内发现氨苄青霉素结合位点以来，许多注意力都集中在通道的潜在特异性上，其中结合位点被假定为促进或阻碍β-内酰胺类药物的渗透。由于早期的研究孔蛋白的渗透性没有知识的多药外排泵的贡献，在整个通量过程中通过细胞被膜，在这项研究中，我们仔细研究了孔蛋白的渗透性和主动外排的氨苄青霉素和苄青霉素。我们发现，流入发生明显的自发被动扩散，没有任何迹象表明，在浓度范围内的特异性结合相关的抗生素作用的这些药物，氨苄青霉素的较高的渗透性是完全预期从总的属性，这种药物作为一种两性离子化合物。AcrAB的主动外排对青霉素具有较强的亲和性和高度的正协同作用。我们的数据现在给出了这两种化合物的流入，流出和周质降解（由AmpC β-内酰胺酶催化）的完整定量图片，并与此处使用的大肠杆菌菌株的敏感性密切相关，从而不仅验证了我们的模型，而且验证了本研究中获得的参数。
Small, hydrophilic compounds such as beta-lactams diffuse across the outer membrane of Gram-negative bacteria through porin channels, which were originally thought to be nonspecific channels devoid of any specificity. However, since the discovery of an ampicillin-binding site within the OmpF channel in 2002, much attention has been focused on the potential specificity of the channel, where the binding site was assumed either to facilitate or to retard the penetration of beta-lactams. Since the earlier studies on porin permeability were done without the knowledge of the contribution of multidrug efflux pumps in the overall flux process across the cell envelope, in this study we have carefully studied both the porin permeability and active efflux of ampicillin and benzylpenicillin. We found that the influx occurs apparently by a spontaneous passive diffusion without any indication of specific binding within the concentration range relevant to the antibiotic action of these drugs, and that the higher permeability for ampicillin is totally as expected from the gross property of this drug as a zwitterionic compound. The active efflux by AcrAB was more effective for benzylpenicillin due to the stronger affinity and high degree of positive cooperativity. Our data now give a complete quantitative picture of the influx, efflux, and periplasmic degradation (catalyzed by AmpC beta-lactamase) of these two compounds, and correlate closely with the susceptibility of Escherichia coli strains used here, thus validating not only our model but also the parameters obtained in this study.