Effect of divalent cation removal on the structure of gram-negative bacterial outer membrane models.
Effect of divalent cation removal on the structure of gram-negative bacterial outer membrane models.
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DOI：
10.1021/la504407v
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
Lakey JH
中科院分区：
文献类型：
--
作者：
Clifton LA;Skoda MW;Le Brun AP;Ciesielski F;Kuzmenko I;Holt SA;Lakey JH
革兰氏阴性细菌外膜（GNB-OM）的脂质组成是不对称的，具有富含磷脂的内小叶和主要由脂多糖（LPS）组成的外小叶。LPS是聚阴离子分子，在脂质A和核心寡糖区域中存在大量磷酸基团。由于负电荷的积累而产生的排斥力被二价阳离子（Mg 2+和Ca 2+）屏蔽和桥接，已知二价阳离子对细菌OM的完整性至关重要。事实上，二价阳离子的螯合是一种完善的渗透革兰氏阴性细菌如大肠杆菌的方法。在这里，我们使用X射线和中子反射率（XRR和NR，分别）技术来检查模型GNB-OM的稳定性中的钙离子的作用。使用XRR，我们表明，Ca 2+结合到粗糙突变体LPS（RaLPS）膜的核心区域，产生更有序的结构相比，二价阳离子自由单分子膜。使用最近开发的GNB-OM的固体支撑模型，我们研究了钙去除对DPPC：RaLPS双层膜的不对称性的影响。我们表明，没有二价阳离子的电荷屏蔽效应，LPS被迫克服的philically不利的能量障碍和翻转的疏水双层，以尽量减少排斥静电力，导致约20%的混合LPS和DPPC之间的内部和外部双层小叶。这些结果首次揭示了二价阳离子稳定外膜的众所周知的机制背后的分子细节。这证实了不对称模型对于未来外膜稳定性和抗生素渗透研究的相关性。
The Gram-negative bacterial outer membrane (GNB-OM) is asymmetric in its lipid composition with a phospholipid-rich inner leaflet and an outer leaflet predominantly composed of lipopolysaccharides (LPS). LPS are polyanionic molecules, with numerous phosphate groups present in the lipid A and core oligosaccharide regions. The repulsive forces due to accumulation of the negative charges are screened and bridged by the divalent cations (Mg2+ and Ca2+) that are known to be crucial for the integrity of the bacterial OM. Indeed, chelation of divalent cations is a well-established method to permeabilize Gram-negative bacteria such as Escherichia coli. Here, we use X-ray and neutron reflectivity (XRR and NR, respectively) techniques to examine the role of calcium ions in the stability of a model GNB-OM. Using XRR we show that Ca2+ binds to the core region of the rough mutant LPS (RaLPS) films, producing more ordered structures in comparison to divalent cation free monolayers. Using recently developed solid-supported models of the GNB-OM, we study the effect of calcium removal on the asymmetry of DPPC:RaLPS bilayers. We show that without the charge screening effect of divalent cations, the LPS is forced to overcome the thermodynamically unfavorable energy barrier and flip across the hydrophobic bilayer to minimize the repulsive electrostatic forces, resulting in about 20% mixing of LPS and DPPC between the inner and outer bilayer leaflets. These results reveal for the first time the molecular details behind the well-known mechanism of outer membrane stabilization by divalent cations. This confirms the relevance of the asymmetric models for future studies of outer membrane stability and antibiotic penetration.
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DOI：
10.1016/0006-291x(65)90191-9
发表时间：
1965-01-01
影响因子：
3.1
作者：
LEIVE, L
通讯作者：
LEIVE, L
DOI：
10.1006/bbrc.1998.9773
发表时间：
1998-12-09
影响因子：
3.1
作者：
Aurell, CA;Wistrom, AO
通讯作者：
Wistrom, AO
影响因子：
3.4
作者：
Jeworrek, Christoph;Evers, Florian;Winter, Roland
通讯作者：
Winter, Roland
DOI：
10.1051/rphysap:01980001503076100
发表时间：
1980-01-01
期刊：
REVUE DE PHYSIQUE APPLIQUEE
影响因子：
--
作者：
NEVOT, L;CROCE, P
通讯作者：
CROCE, P
影响因子：
3.9
作者：
Callow, P.;Fragneto, G.;Lawrence, M. J.
通讯作者：
Lawrence, M. J.