Synthetic, sequence-random polymers that feature a wide range of backbone and side chain structures have been reported to function as mimics of natural host-defense peptides, inhibiting bacterial growth while exerting little or no toxicity toward eukaryotic cells. The common themes among these materials are net positive charge, which is thought to confer preferential action toward prokaryotic vs eukaryotic cells, and the presence of hydrophobic components, which are thought to mediate membrane disruption. This study is based on a set of new binary cationic-hydrophobic nylon-3 copolymers that was designed to ask whether factors beyond net charge and net hydrophobicity influence the biological activity profile. In previous work, we found that nonpolar subunits preorganized by a ring led to copolymers with a diminished tendency to disrupt human cell membranes (as measured via lysis of red blood cells) relative to copolymers containing more flexible nonpolar subunits. An alternative mode of conformational restriction, involving geminal substitution, also minimized hemolysis. Here, we asked whether combining a cyclic constraint and geminal substitution would be synergistic; the combination was achieved by introducing backbone methyl groups to previously described cyclopentyl and cyclohexyl subunits. The new cyclic subunits containing two quaternary backbone carbons (i.e, two sites of geminal substitution) were comparable or slightly superior in terms of antibacterial potency but markedly superior in terms of low hemolytic activity, relative to cyclic subunits lacking the quaternary carbons. However, new cyclic units containing only one quaternary carbon were very hemolytic, which was unanticipated. Variations in net hydrophobicity cannot explain the trend in hemolysis, in contrast to the standard perspective in this field. The impact of each new polymer on live E. coli cells was evaluated via fluorescence microscopy. All new polymers moved rapidly across the outer membrane without large-scale disruption of barrier function. Increasing the number of quaternary carbons in the nonpolar subunit correlated with an increased propensity to permeabilize the cytoplasmic membrane of E. coli cells. Collectively, these findings show that relationships between nonpolar subunit identity and biological activity are influenced by factors in addition to hydrophobicity and charge. We propose that the variation of subunit conformational properties may be one such factor.

中文翻译：

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Nylon-3 共聚物疏水亚基变异对原核和真核生物膜活性的不同影响

据报道，具有多种主链和侧链结构的合成、序列随机聚合物可作为天然宿主防御肽的模拟物，抑制细菌生长，同时对真核细胞几乎没有毒性或没有毒性。这些材料的共同主题是净正电荷，这被认为对原核细胞和真核细胞具有优先作用，以及疏水成分的存在，这被认为是介导膜破坏的。本研究基于一组新的二元阳离子疏水尼龙 3 共聚物，旨在询问净电荷和净疏水性以外的因素是否会影响生物活性分布。在之前的工作中，通过溶解红细胞）相对于含有更多柔性非极性亚基的共聚物。另一种构象限制模式，包括双胞胎取代，也使溶血最小化。在这里，我们询问将循环约束和双子替换相结合是否会产生协同作用；该组合是通过将主链甲基基团引入先前描述的环戊基和环己基亚基来实现的。包含两个四元骨架碳的新环状亚基（即两个孪生位点）取代）相对于缺乏季碳的环状亚基而言，在抗菌效力方面相当或略胜一筹，但在低溶血活性方面明显优越。然而，仅包含一个季碳的新环状单元具有很强的溶血性，这是出乎意料的。与该领域的标准观点相反，净疏水性的变化不能解释溶血的趋势。通过评估每种新聚合物对活大肠杆菌细胞的影响荧光显微镜。所有新聚合物都迅速穿过外膜，而不会大规模破坏屏障功能。增加非极性亚基中季碳的数量与增加渗透大肠杆菌细胞的细胞质膜的倾向相关。总的来说，这些发现表明非极性亚基身份和生物活性之间的关系受疏水性和电荷之外的因素影响。我们提出亚基构象特性的变化可能是这样一个因素。