The effect of bacteriorhodopsin (BR) on the percolation properties of dimyristoylphosphatidylcholine/distearoylphosphatidylcholine bilayers was examined by studying the quenching of a lipid-bound fluorophore by a lipid-bound quencher, and by spin-spin interactions of a nitroxide-labeled lipid using electron spin resonance (ESR). At the low concentrations of BR used, differential scanning calorimetry showed that although the transition enthalpy was reduced in a concentration-dependent manner by incorporation of BR, the solidus and fluidus phase boundaries and overall shape of the heat capacity profiles were essentially unchanged. However, fluorescence quenching and spin-label ESR data showed that the domain topology, as reflected in the percolation properties, is strongly affected by the protein. In contrast to our previous fluorescence data for the pure lipid mixtures, quenching in the coexistence region is independent of the fluid phase fraction when BR is present. In addition, the percolation threshold estimated by spin-label ESR is shifted in the presence of BR to a higher gel phase fraction at a given lipid composition. Both the fluorescence quenching and spin-label ESR data, together with the results of earlier simulations, strongly suggest that the fluid phase domains are substantially larger and/or less ramified in the presence of BR than in its absence. We have previously reported a similar effect of a transmembrane peptide, pOmpA (Escherichia coli outer membrane protein A signal peptide), on fluid domain connectivity in binary phosphatidylcholine mixtures.

译文

通过研究脂质结合的猝灭剂对脂质结合的荧光团的猝灭以及使用电子自旋的一氧化氮标记的脂质的自旋旋转相互作用,研究了细菌视紫红质(BR)对二肉豆蔻酰基磷脂酰胆碱/二硬脂酰磷脂酰胆碱双层渗透特性的影响。共振(ESR)。在使用低浓度的BR时,差示扫描量热法显示,尽管通过掺入BR以一定的浓度依赖性降低了转变焓,但固相线和液相线的边界和热容曲线的总体形状基本不变。但是,荧光猝灭和自旋标记ESR数据表明,渗透特性所反映的域拓扑结构受到蛋白质的强烈影响。与我们以前的纯脂质混合物的荧光数据相反,当存在BR时,共存区域的猝灭与液相分数无关。另外,在给定脂质组成下,在BR的存在下,自旋标记ESR估计的渗透阈值会转移到较高的凝胶相分数。荧光猝灭和自旋标记ESR数据以及早期模拟的结果都强烈表明,在存在BR的情况下,与不存在BR的情况相比,液相域的分支和/或分枝显着增加。我们以前曾报道过跨膜肽pOmpA(大肠杆菌外膜蛋白A信号肽)对二元磷脂酰胆碱混合物中的流体域连通性具有类似作用。

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