Institute of Pharmacy, Martin-Luther-University Halle-Wittenberg, D-06120 Halle/Saale, Germany.
J Am Chem Soc. 2012 Mar 7;134(9):4324-31. doi: 10.1021/ja2108382. Epub 2012 Feb 22.
We present a detailed analysis of the behavior of the highly flexible post-translational lipid modifications of rhodopsin from multiple-microsecond all-atom molecular dynamics simulations. Rhodopsin was studied in a realistic membrane environment that includes cholesterol, as well as saturated and polyunsaturated lipids with phosphocholine and phosphoethanolamine headgroups. The simulation reveals striking differences between the palmitoylations at Cys322 and Cys323 as well as between the palmitoyl chains and the neighboring lipids. Notably the palmitoyl group at Cys322 shows considerably greater contact with helix H1 of rhodopsin, yielding frequent chain upturns with longer reorientational correlation times, and relatively low order parameters. While the palmitoylation at Cys323 makes fewer protein contacts and has increased order compared to Cys322, it nevertheless exhibits greater flexibility with smaller order parameters than the stearoyl chains of the surrounding lipids. The dynamical structure of the palmitoylations-as well as their extensive fluctuations-suggests a complex function for the post-translational modifications in rhodopsin and potentially other G protein-coupled receptors, going beyond their role as membrane anchoring elements. Rather, we propose that the palmitoylation at Cys323 has a potential role as a lipid anchor, whereas the palmitoyl-protein interaction observed for Cys322 suggests a more specific interaction that affects the stability of the dark state of rhodopsin.
我们从多微秒全原子分子动力学模拟中对高度灵活的视紫红质翻译后脂质修饰的行为进行了详细分析。视紫红质在包含胆固醇以及带有磷酸胆碱和磷酸乙醇胺头基的饱和和多不饱和脂质的真实膜环境中进行了研究。该模拟揭示了 Cys322 和 Cys323 处的棕榈酰化以及棕榈酰链与相邻脂质之间的惊人差异。值得注意的是，Cys322 处的棕榈酰基与视紫红质的 H1 螺旋有相当大的接触，导致频繁的链向上翻转和较长的重新取向相关时间，以及相对较低的有序参数。虽然 Cys323 处的棕榈酰化与 Cys322 相比与蛋白质的接触较少，有序性增加，但与周围脂质的硬脂酰链相比，它具有更大的灵活性和较小的有序参数。棕榈酰化的动力学结构及其广泛的波动表明，翻译后修饰对视紫红质和潜在的其他 G 蛋白偶联受体具有复杂的功能，超出了其作为膜锚定元件的作用。相反，我们提出 Cys323 的棕榈酰化可能具有作为脂质锚的潜在作用，而 Cys322 观察到的棕榈酰-蛋白相互作用表明存在更具体的相互作用，影响视紫红质的暗态稳定性。
