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首页> 外文期刊>Biochemistry >Position and Ionization State of Asp in the Core of Membrane-Inserted a Helices Control Both the Equilibrium between Transmembrane and Nontransmembrane Helix Topography and Transmembrane Helix Positioning
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Position and Ionization State of Asp in the Core of Membrane-Inserted a Helices Control Both the Equilibrium between Transmembrane and Nontransmembrane Helix Topography and Transmembrane Helix Positioning

机译：Asp在膜插入螺旋中心中的位置和电离状态控制跨膜和非跨膜螺旋形貌之间的平衡以及跨膜螺旋形定位

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摘要

The behavior of model-membrane-inserted polyLeu-rich peptides containing Asp residues located at various positions in their hydrophobic core was investigated.The topography of the bilayer-inserted a helices formed by these peptides was evaluated by measuring the emission lambda_(max) and quenching the fluorescence of a Trp at the center of the peptide sequence.When Asp residues were protonated (at low pH),peptides that were incorporated into vesicles composed of dioleoylphosphatidylcholine (DOPC) adopted a topography in which the polyLeu sequence predominantly formed a normal transmembrane (TM) helix.When Asp residues were ionized (at neutral or high pH),topography was altered in a manner that would allow the charged Asp residues to reside near the bilayer surface.In DOPC vesicles,most peptides repositioned so that the longest segment of consecutive hydrophobic residues (12 residue minimum) formed a truncated/shifted TM structure.However,peptides with one or two charged Asp residues close to the center of the hydrophobic sequence and thus lacking even a 12-residue continuous hydrophobic segment,formed a helical non-TM state locating near the bilayer surface.At low pH,incorporation of the peptides into thicker bilayers composed of dierucoylphosphatidylcholine (DEuPC) resulted in the formation of a mixture of the normal TM state and the non-TM helical state located near the bilayer surface.In DEuPC vesicles at high pH,the non-TM state tended to predominate.How Asp-ionization-dependent shifts in helix topography may regulate the function of membrane proteins exposed to environments with differing pH in vivo (e.g.,endosomes) is discussed.
机译：研究了模型膜插入的富含AsL残基位于疏水核心不同位置的富含PolyLeu的肽的行为。通过测量发射Lambda_（max）和发射率来评估双层插入的由这些肽形成的螺旋的形貌。在肽序列的中心淬灭Trp的荧光（TM）螺旋。当Asp残基被离子化（在中性或高pH下）时，拓扑结构以允许带电Asp残基位于双层表面附近的方式改变。在DOPC囊泡中，大多数肽会重新定位，从而使最长的片段连续的疏水残基（最少12个残基）之间形成一个截断/移位的TM结构。处于疏水序列的中心，因此甚至没有12个残基的连续疏水链段，在双层表面附近形成了螺旋的非TM状态。在低pH值下，将肽掺入由二十二烷基酰磷脂酰胆碱（DEuPC）组成的较厚双层中导致在双层表面附近形成正常TM状态和非TM螺旋状态的混合物。在高pH的DEuPC囊泡中，非TM状态趋于占优势.Asp电离依赖性螺旋如何移动形貌可调节暴露于体内不同pH值环境（例如，内体）的膜蛋白的功能。

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