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首页> 外文期刊>Biochemistry >Plasma factors required for human apolipoprotein A-II dimerization.
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Plasma factors required for human apolipoprotein A-II dimerization.

机译：人载脂蛋白A-II二聚化所需的血浆因子。

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摘要

Although plasma high-density lipoproteins (HDL) have been implicated in several cardioprotective pathways, the physiologic role of apolipoprotein (apo) A-II, the second most abundant of the HDL proteins, remains ambiguous. Human apo A-II is distinguished from most other species by a single cysteine (Cys6), which forms a disulfide bond with other cysteine-containing apos. In human plasma, nearly all apo A-II occurs as disulfide-linked homodimers of 17.4 kDa. Although dimerization is an important determinant of human apo A-II metabolism, its mechanism and the plasma and/or cellular sites of its dimerization are not known. Using SDS-PAGE and densitometry we investigated the kinetics of apo A-II dimerization and observed a slow (t(1/2) = approximately 10 days), second-order process in Tris-buffered saline. In 3 M guanidine hydrochloride, which disrupts apo A-II secondary structure and self-association, the rate was 3-fold slower. In contrast, lipid surfaces that promote apo A-II alpha-helix formation and lipophilic interaction profoundly enhanced the rate. Reassembled HDL increased the second-order rate constant k(2) by 7500-fold, unilamellar 1-palmitoyl-2-oleoylphosphatidylcholine vesicles increased k(2) 850-fold, and physiological concentrations of human serum albumin increased k(2) 220-fold. Thus, while dimerization of apo A-II in aqueous buffer is too slow to account for the high fraction of dimer found in plasma, lipids and proteins "catalyze" dimer formation, a process that could occur either intracellularly prior to secretion or in the plasma compartment following secretion. These data suggest that formation of disulfide links within or between polypeptide chains can be controlled, in part, by coexisting lipids and proteins.
机译：尽管血浆高密度脂蛋白（HDL）与多种心脏保护途径有关，但载脂蛋白（apo）A-II（第二高含量的HDL蛋白）的生理作用仍然不明确。人载脂蛋白A-II与大多数其他物种的区别在于单个半胱氨酸（Cys6），该半胱氨酸与其他含半胱氨酸的’形成二硫键。在人血浆中，几乎所有载脂蛋白A-II都以17.4 kDa的二硫键连接的同型二聚体形式存在。尽管二聚化是人类载脂蛋白A-II代谢的重要决定因素，但其二聚作用的机理以及血浆和/或细胞部位尚不清楚。使用SDS-PAGE和光密度测定法，我们研究了载脂蛋白A-II二聚化的动力学，并在Tris缓冲盐水中观察到了缓慢的（t（1/2）=约10天）二阶过程。在3M盐酸胍中，它破坏apo A-II二级结构和自缔合，其速度慢了3倍。相反，促进载脂蛋白A-IIα-螺旋形成和亲脂性相互作用的脂质表面会大大提高该速率。重新组装的HDL将二阶速率常数k（2）增加了7500倍，单层的1-palmitoyl-2-oleoylphosphatidylcholine囊泡增加了k（2）850倍，并且人血清白蛋白的生理浓度增加了k（2）220-折。因此，尽管在水性缓冲液中载脂蛋白A-II的二聚化太慢而无法说明血浆中发现的高浓度二聚体，但是脂质和蛋白质“催化”了二聚体的形成，该过程可能在分泌前在细胞内或在血浆中发生分泌后的隔室。这些数据表明，多肽链内或多肽链之间的二硫键的形成可以部分地通过脂质和蛋白质的共存来控制。

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