Alpha-Crystallin Association with the Model of Human and Animal Eye Lens-Lipid Membranes is Modulated by Surface Hydrophobicity of Membranes.

This research aims to probe the interaction of α-crystallin with a model of human, porcine, and mouse lens-lipid membranes. Cholesterol/model of human lens-lipid (Chol/MHLL), cholesterol/model of porcine lens-lipid (Chol/MPLL), and cholesterol/model of mouse lens-lipid (Chol/MMLL) membranes with 0 to 60 mol% Chol were prepared using the rapid solvent exchange method and probe-tip sonication. The hydrophobicity near the surface of model lens-lipid membranes and α-crystallin association with these membranes were investigated using the electron paramagnetic resonance spin-labeling approach. With increased Chol content, the hydrophobicity near the surface of Chol/MHLL, Chol/MPLL, and Chol/MMLL membranes, the maximum percentage of membrane surface occupied (MMSO) by α-crystallin, and the association constant (Ka) decreased, showing that surface hydrophobicity of model lens-lipid membranes modulated the α-crystallin association with these membranes. The different MMSO and Ka for different model lens-lipid membranes with different rates of decrease of MMSO and Ka with increased Chol content and decreased hydrophobicity near the surface of these membranes suggested that the lipid composition also modulates α-crystallin association with membranes. Despite different lipid compositions, complete inhibition of α-crystallin association with model lens-lipid membranes was observed at saturating Chol content forming cholesterol bilayer domains (CBDs) with the lowest hydrophobicity near the surface of these membranes. The decreased mobility parameter with increased α-crystallin concentration suggested that membranes near the surface became less mobile due to α-crystallin association. The decreased mobility parameter and increased maximum splitting with increased Chol content suggested that membranes became less mobile and more ordered near the surface with increased Chol content. This study suggested that the interaction of α-crystallin with model lens-lipid membranes is hydrophobic. Furthermore, our data indicated that Chol and CBDs reduce α-crystallin association with lens membrane, likely increase α-crystallin concentration in lens cytoplasm, and possibly favor the chaperone-like activity of α-crystallin maintaining lens cytoplasm homeostasis.

本研究旨在探究α-晶状体蛋白与人类、猪和小鼠晶状体脂质膜模型的相互作用。 采用快速溶剂交换法和探头超声法制备了胆固醇/人类晶状体脂质模型（Chol/MHLL）、胆固醇/猪晶状体脂质模型（Chol/MPLL）和胆固醇/小鼠晶状体脂质模型（Chol/MMLL）膜，其中胆固醇含量为0至60摩尔%。利用电子顺磁共振自旋标记法研究了模型晶状体脂质膜表面附近的疏水性以及α-晶状体蛋白与这些膜的结合情况。 随着胆固醇含量的增加，Chol/MHLL、Chol/MPLL和Chol/MMLL膜表面附近的疏水性、α-晶状体蛋白占据膜表面的最大百分比（MMSO）以及结合常数（Ka）均降低，这表明模型晶状体脂质膜的表面疏水性调节了α-晶状体蛋白与这些膜的结合。不同模型晶状体脂质膜的MMSO和Ka不同，随着胆固醇含量增加和膜表面附近疏水性降低，MMSO和Ka的降低速率也不同，这表明脂质成分也调节α-晶状体蛋白与膜的结合。尽管脂质成分不同，但在胆固醇饱和含量时，观察到α-晶状体蛋白与模型晶状体脂质膜的结合完全被抑制，此时形成胆固醇双层结构域（CBDs），膜表面附近的疏水性最低。随着α-晶状体蛋白浓度增加，迁移率参数降低，这表明由于α-晶状体蛋白的结合，膜表面附近的膜流动性降低。随着胆固醇含量增加，迁移率参数降低且最大分裂值增加，这表明随着胆固醇含量增加，膜表面附近的膜流动性降低且更有序。 本研究表明α-晶状体蛋白与模型晶状体脂质膜的相互作用是疏水性的。此外，我们的数据表明胆固醇和CBDs减少了α-晶状体蛋白与晶状体膜的结合，可能会增加晶状体细胞质中α-晶状体蛋白的浓度，并可能有利于α-晶状体蛋白发挥类似分子伴侣的活性，维持晶状体细胞质的内稳态。