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Conformation and lipid binding properties of peptide models of exchangeable apolipoproteins.

机译：可交换载脂蛋白肽模型的构象和脂质结合特性。

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摘要

Lipoproteins solubilize and transport lipids and cholesterol in the body. They contain proteins (apolipoproteins) that function structurally, as cofactors for enzymes, and in receptor binding. The exchangeable apolipoproteins traffic between lipoproteins and share a sequence pattern of two types (A and B) of eleven-residue amphipathic alpha-helical repeats, thought to be lipid-binding elements. Because of conformational flexibility of exchangeable apolipoproteins, peptide models have been used to study the properties of these repeats. Two overlapping 44-residue (ABAB) real sequence peptides (RSP-1, residues 99--142, and RSP-2, 121--163) from the sequence of apolipoprotein A-I and two 22-residue consensus sequence peptides (CSP-AB and CSP-BA), designed as organizational rearrangements of consensus A and B repeats, were studied. Peptide conformation and thermal stability were studied using circular dichroism and the lipid-binding properties of the RSPs were analyzed using density gradient sedimentation and electron microscopy. In phosphate buffer, RSP-1 was 23% helical while RSP-2 was unstructured even though they have 50% sequence overlap. Helical structure could be induced in both peptides (up to 75% for RSP-1 and 50% for RSP-2) in lipid-mimicking detergent or structure-promoting solvents. The secondary structure of RSP-1 was insensitive to pH, but RSP-2 showed a loss of helical content in detergent at acidic pH, possibly due to two histidine residues that lie in the hydrophobic face of its second AB repeat. Both peptides bound and solubilized phospholipid, with RSP-1 having higher affinity than RSP-2. The particles formed depended upon the peptide-to-lipid ratio and both vesicular and phospholipid bilayer discoidal particles, similar to the nascent form of HDL, were observed. Furthermore, RSP-1 formed more discoidal particles than RSP-2, consistent with their different lipid affinities. CSP-AB in phosphate buffer showed 26% helical structure that increased up to 50% in detergent or solvents, while CSP-BA was unstructured in phosphate buffer and could only be induced to adopt 30% helix. This work further elucidates the conformational and lipid-binding properties of the helical lipid-binding repeats of exchangeable apolipoproteins by defining the different lipid affinities of homologous repeated sequences and the effect of organizational arrangement of the repeats.
机译：脂蛋白在体内溶解和运输脂质和胆固醇。它们包含蛋白质（载脂蛋白），该蛋白质在结构上起酶的辅助因子作用，并与受体结合。脂蛋白之间可交换的载脂蛋白运输，并共有11种残基两亲性α螺旋重复序列的两种类型（A和B）的序列模式，被认为是脂质结合元件。由于可交换载脂蛋白的构象灵活性，已使用肽模型研究这些重复序列的特性。来自载脂蛋白AI序列的两个重叠的44残基（ABAB）真实序列肽（RSP-1，残基99--142和RSP-2，121--163）和两个22残基的共有序列肽（CSP-AB和CSP-BA）进行了研究，该设计被设计为共识A和B重复的组织重排。使用圆二色性研究了肽的构象和热稳定性，并使用密度梯度沉降和电子显微镜分析了RSP的脂质结合特性。在磷酸盐缓冲液中，尽管RSP-1具有50％的序列重叠，但RSP-1却是23％的螺旋状。在模拟脂质的去污剂或促进结构的溶剂中，两种肽均可诱导螺旋结构（对于RSP-1高达75％，对于RSP-2高达50％）。 RSP-1的二级结构对pH不敏感，但RSP-2在酸性pH下显示去污剂中的螺旋含量降低，这可能是由于位于其第二个AB重复序列疏水面上的两个组氨酸残基所致。两种肽都结合并溶解了磷脂，RSP-1的亲和力高于RSP-2。形成的颗粒取决于肽与脂质的比率，并且观察到类似于新生形式的HDL的囊泡和磷脂双层盘状颗粒。此外，RSP-1比RSP-2形成更多的盘状颗粒，这与其脂质亲和力不同是一致的。磷酸盐缓冲液中的CSP-AB表现出26％的螺旋结构，在去污剂或溶剂中最多可增加50％，而CSP-BA在磷酸盐缓冲液中是非结构化的，只能被诱导采用30％的螺旋。这项工作通过定义同源重复序列的不同脂质亲和力和重复序列的组织安排，进一步阐明了可交换载脂蛋白的螺旋脂质结合重复序列的构象和脂质结合特性。

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  • 作者

    Wally, Jeremy Loren.;

  • 作者单位

    Boston University.;

  • 授予单位 Boston University.;
  • 学科 Biophysics General.
  • 学位 Ph.D.
  • 年度 2005
  • 页码 298 p.
  • 总页数 298
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 生物物理学;
  • 关键词

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