Biomolecular Sciences Graduate Programs, Boise State University, Boise, ID 83725, USA.
Department of Physics, Boise State University, Boise, ID 83725, USA.
Int J Mol Sci. 2023 Sep 2;24(17):13600. doi: 10.3390/ijms241713600.
Several discoveries show that with age and cataract formation, β-crystallin binds with the lens membrane or associates with other lens proteins, which bind with the fiber cell plasma membrane, accompanied by light scattering and cataract formation. However, how lipids (phospholipids and sphingolipids) and cholesterol (Chol) influence β-crystallin binding to the membrane is unclear. This research aims to elucidate the role of lipids and Chol in the binding of β-crystallin to the membrane and the membrane's physical properties (mobility, order, and hydrophobicity) with β-crystallin binding. We used electron paramagnetic resonance (EPR) spin-labeling methods to investigate the binding of β-crystallin with a model of porcine lens-lipid (MPLL), model of mouse lens-lipid (MMLL), and model of human lens-lipid (MHLL) membrane with and without Chol. Our results show that β-crystallin binds with all of the investigated membranes in a saturation manner, and the maximum parentage of the membrane surface occupied (MMSO) by β-crystallin and the binding affinity (K) of β-crystallin to the membranes followed trends: MMSO (MPLL) > MMSO (MMLL) > MMSO (MHLL) and K (MHLL) > K (MMLL) ≈ K (MPLL), respectively, in which the presence of Chol reduces the MMSO and K for all membranes. The mobility near the headgroup regions of the membranes decreases with an increase in the binding of β-crystallin; however, the decrease is more pronounced in the MPLL and MMLL membranes than the MHLL membrane. In the MPLL and MMLL membranes, the membranes become slightly ordered near the headgroup with an increase in β-crystallin binding compared to the MHLL membrane. The hydrophobicity near the headgroup region of the membrane increases with β-crystallin binding; however, the increase is more pronounced in the MPLL and MMLL membranes than the MHLL membrane, indicating that β-crystallin binding creates a hydrophobic barrier for the passage of polar molecules, which supports the barrier hypothesis in cataract formation. However, in the presence of Chol, there is no significant increase in hydrophobicity with β-crystallin binding, suggesting that Chol prevents the formation of a hydrophobic barrier, possibly protecting against cataract formation.
几项发现表明，随着年龄的增长和白内障的形成，β-晶状体蛋白与晶状体膜结合或与其他晶状体蛋白结合，与纤维细胞膜结合，伴随着光散射和白内障的形成。然而，脂质（磷脂和鞘脂）和胆固醇（Chol）如何影响β-晶状体蛋白与膜的结合尚不清楚。本研究旨在阐明脂质和 Chol 在β-晶状体蛋白与膜结合以及膜的物理性质（流动性、有序性和疏水性）与β-晶状体蛋白结合中的作用。我们使用电子顺磁共振（EPR）自旋标记方法研究了β-晶状体蛋白与猪晶状体脂质（MPLL）模型、鼠晶状体脂质（MMLL）模型和人晶状体脂质（MHLL）模型以及有无胆固醇（Chol）的膜的结合。我们的结果表明，β-晶状体蛋白以饱和的方式与所有研究的膜结合，β-晶状体蛋白占据膜表面的最大比例（MMSO）和β-晶状体蛋白与膜的结合亲和力（K）遵循以下趋势：MMSO（MPLL）>MMSO（MMLL）>MMSO（MHLL）和 K（MHLL）>K（MMLL）≈K（MPLL），其中 Chol 的存在降低了所有膜的 MMSO 和 K。随着β-晶状体蛋白结合的增加，靠近膜头部区域的流动性降低；然而，在 MPLL 和 MMLL 膜中，这种降低比在 MHLL 膜中更为明显。在 MPLL 和 MMLL 膜中，与 MHLL 膜相比，随着β-晶状体蛋白结合的增加，靠近头部的膜变得稍微有序。随着β-晶状体蛋白结合的增加，靠近头部区域的膜疏水性增加；然而，在 MPLL 和 MMLL 膜中，这种增加比在 MHLL 膜中更为明显，这表明β-晶状体蛋白结合为极性分子的通过形成了一个疏水屏障，这支持了白内障形成中的屏障假说。然而，在存在 Chol 的情况下，随着β-晶状体蛋白结合，疏水性没有显著增加，这表明 Chol 阻止了疏水屏障的形成，可能防止了白内障的形成。
