Interaction of alpha-crystallin with four major phospholipids of eye lens membranes.
Interaction of alpha-crystallin with four major phospholipids of eye lens membranes.
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α-晶状体蛋白与眼晶状体膜的四种主要磷脂的相互作用。
DOI：
10.1016/j.exer.2020.108337
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发表时间：
2021-01
影响因子：
3.4
通讯作者：
Mainali L
中科院分区：
文献类型：
--
作者：
Timsina R;Khadka NK;Maldonado D;Mainali L
研究表明，白内障形成的重要因素是主要的晶状体蛋白α-晶状体蛋白与晶状体纤维细胞质膜的结合。晶状体纤维细胞质膜由四种主要的磷脂（PLs）组成，即磷脂酰胆碱（PC）、磷脂酰乙醇胺（PE）、磷脂酰丝氨酸（PS）和鞘磷脂（SM）。尽管多次尝试研究α-晶状体蛋白与晶状体膜磷脂的相互作用，但单个磷脂在与α-晶状体蛋白结合中的作用仍不清楚。我们最近开发了电子顺磁共振（EPR）自旋标记方法来研究α-晶状体蛋白与PC膜的结合。在此，我们使用最近开发的EPR方法明确测量α-晶状体蛋白与单个（PE*、PS和SM）以及两种成分混合物（SM/PE、SM/PS和SM/PC，摩尔比分别为70:30和50:50）的磷脂膜的结合亲和力（Ka），以及这些膜在与α-晶状体蛋白结合后的物理性质（流动性参数和最大分裂）。这项研究的一个关键发现是，α-晶状体蛋白与单个磷脂膜结合的Ka呈现以下趋势：Ka(PC)>Ka(SM)>Ka(PS)>Ka(PE*)，表明PE*对结合的抑制作用最强，而PC的抑制作用最弱。此外，α-晶状体蛋白与磷脂膜两种成分混合物结合的Ka呈现以下趋势：Ka(SM/PE)>Ka(SM/PS)>Ka(SM/PC)，表明SM/PC对结合的抑制作用最强，而SM/PE的抑制作用最弱。除了PE*膜（α-晶状体蛋白不与其结合）外，所有其他膜的流动性参数都随着α-晶状体蛋白浓度的增加而降低。这表明当越来越多的α-晶状体蛋白与膜结合时，膜在磷脂头部区域附近变得更加固定。只有SM和SM/PE（70:30摩尔比）膜的最大分裂随着α-晶状体蛋白结合的增加而增加。这表明这些膜的磷脂头部区域在α-晶状体蛋白与这些膜结合后变得更加有序。我们的结果表明，α-晶状体蛋白以可饱和的方式与磷脂膜结合。此外，我们的数据表明，α-晶状体蛋白与磷脂膜的结合可能是通过α-晶状体蛋白与膜的疏水脂肪酸核心之间的疏水相互作用发生的，并且这种相互作用受磷脂头部基团的大小和电荷、头部基团之间的氢键以及磷脂曲率的调节。因此，这项研究深入了解了α-晶状体蛋白与由晶状体膜四种主要磷脂的单个和两种成分混合物组成的磷脂膜的相互作用。
It is well-studied that the significant factor in cataract formation is the association of α-crystallin, a major eye lens protein, with the fiber cell plasma membrane of the eye lens. The fiber cell plasma membrane of the eye lens consists of four major phospholipids (PLs), i.e., phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), and sphingomyelin (SM). Despite several attempts to study the interaction of α-crystallin with PLs of the eye lens membrane, the role of individual PL for the binding with α-crystallin is still unclear. We recently developed the electron paramagnetic resonance (EPR) spin-labeling method to study the binding of α-crystallin to the PC membrane. Here, we use the recently developed EPR method to explicitly measure the binding affinity (Ka) of α-crystallin to the individual (PE*, PS, and SM) and two-component mixtures (SM/PE, SM/PS, and SM/PC in 70:30 and 50:50 mol%) of PL membranes as well as the physical properties (mobility parameter and maximum splitting) of these membranes upon binding with α-crystallin. One of the key findings of this study was that the Ka of α-crystallin binding to individual PL membranes followed the trends: Ka(PC) > Ka(SM) > Ka(PS) > Ka(PE*), indicating PE* inhibits binding the most whereas PC inhibits binding the least. Also, the Ka of α-crystallin binding to two-component mixtures of PL membranes followed the trends: Ka(SM/PE) > Ka(SM/PS) > Ka(SM/PC), indicating SM/PC inhibits binding the most whereas SM/PE inhibits binding the least. Except for the PE* membrane, for which there was no binding of α-crystallin, the mobility parameter for all other membranes decreased with an increase in α-crystallin concentration. It represents that the membranes become more immobilized near the headgroup regions of the PLs when more and more α-crystallin binds to them. The maximum splitting increased only for the SM and the SM/PE (70:30 mol%) membranes, with an increase in the binding of α-crystallin. It represents that the PL headgroup regions of these membranes become more ordered after binding of α-crystallin to these membranes. Our results showed that α-crystallin binds to PL membranes in a saturable manner. Also, our data suggest that the binding of α-crystallin to PL membranes likely occurs through hydrophobic interaction between α-crystallin and the hydrophobic fatty acid core of the membranes, and such interaction is modulated by the PL headgroup’s size and charge, hydrogen bonding between headgroups, and PL curvature. Thus, this study provides an in-depth understanding of α-crystallin interaction with the PL membranes made of individual and two-component mixtures of the four major PLs of the eye lens membranes.
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