Biomaterials Department, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany.
Large Scale Structures (LSS) Group, Institut Laue-Langevin, Grenoble, France.
Biophys J. 2018 Apr 10;114(7):1624-1635. doi: 10.1016/j.bpj.2018.02.014.
The outer surfaces of Gram-negative bacteria are composed of lipopolysaccharide (LPS) molecules exposing oligo- and polysaccharides to the aqueous environment. This unique, structurally complex biological interface is of great scientific interest as it mediates the interaction of bacteria with antimicrobial agents as well as with neighboring bacteria in colonies and biofilms. Structural studies on LPS surfaces, however, have so far dealt almost exclusively with rough mutant LPS of reduced molecular complexity and limited biological relevance. Here, by using neutron reflectometry, we structurally characterize planar monolayers of wild-type LPS from Escherichia coli O55:B5 featuring strain-specific O-side chains in the presence and absence of divalent cations and under controlled interaction conditions. The model used for the reflectivity analysis is self-consistent and based on the volume fraction profiles of all chemical components. The saccharide profiles are found to be bimodal, with dense inner oligosaccharides and more dilute, extended O-side chains. For interacting LPS monolayers, we establish the pressure-distance curve and determine the distance-dependent saccharide conformation.
革兰氏阴性菌的外表面由脂多糖 (LPS) 分子组成，这些分子将寡糖和多糖暴露于水相环境中。这种独特的、结构复杂的生物界面具有重要的科学意义，因为它介导了细菌与抗菌剂以及与菌落和生物膜中相邻细菌的相互作用。然而，迄今为止，对 LPS 表面的结构研究几乎完全针对结构简化且生物学相关性有限的粗糙突变 LPS。在这里，我们通过使用中子反射技术，在存在和不存在二价阳离子以及在受控相互作用条件下，对具有菌株特异性 O-侧链的大肠杆菌 O55:B5 野生型 LPS 的平面单层进行结构表征。用于反射率分析的模型是自洽的，并且基于所有化学组分的体积分数分布。发现糖的分布呈双峰型，具有密集的内部寡糖和更稀松、扩展的 O-侧链。对于相互作用的 LPS 单层，我们建立了压力-距离曲线，并确定了距离相关的糖构象。
