Binding of Alpha-Crystallin to Cortical and Nuclear Lens Lipid Membranes Derived from a Single Lens.

Several studies reported that α-crystallin concentrations in the eye lens cytoplasm decrease with a corresponding increase in membrane-bound α-crystallin with age and cataracts. The influence of the lipid and cholesterol composition difference between cortical membrane (CM) and nuclear membrane (NM) on α-crystallin binding to membranes is still unclear. This study uses the electron paramagnetic resonance (EPR) spin-labeling method to investigate the α-crystallin binding to bovine CM and NM derived from the total lipids extracted from a single lens. Compared to CMs, NMs have a higher percentage of membrane surface occupied by α-crystallin and binding affinity, correlating with less mobility and more order below and on the surface of NMs. α-Crystallin binding to CM and NM decreases mobility with no significant change in order and hydrophobicity below and on the surface of membranes. Our results suggest that α-crystallin mainly binds on the surface of bovine CM and NM and such surface binding of α-crystallin to membranes in clear and young lenses may play a beneficial role in membrane stability. However, with decreased cholesterol content within the CM, which mimics the decreased cholesterol content in the cataractous lens membrane, α-crystallin binding increases the hydrophobicity below the membrane surface, indicating that α-crystallin binding forms a hydrophobic barrier for the passage of polar molecules, supporting the barrier hypothesis in developing cataracts.

几项研究报告称，随着年龄增长和白内障的出现，眼晶状体细胞质中的α-晶状体蛋白浓度降低，而膜结合的α-晶状体蛋白相应增加。皮质膜（CM）和核膜（NM）之间脂质和胆固醇组成差异对α-晶状体蛋白与膜结合的影响仍不清楚。本研究采用电子顺磁共振（EPR）自旋标记法，研究从单个晶状体提取的总脂质中获得的牛CM和NM与α-晶状体蛋白的结合情况。与CM相比，NM被α-晶状体蛋白占据的膜表面百分比更高，结合亲和力更强，这与NM下方及表面的流动性更低且更有序相关。α-晶状体蛋白与CM和NM的结合降低了流动性，而膜下方及表面的有序性和疏水性没有显著变化。我们的研究结果表明，α-晶状体蛋白主要结合在牛CM和NM的表面，在透明和年轻晶状体中，α-晶状体蛋白与膜的这种表面结合可能对膜的稳定性起到有益作用。然而，随着CM内胆固醇含量降低（这模拟了白内障晶状体膜中胆固醇含量的降低），α-晶状体蛋白结合增加了膜表面下方的疏水性，这表明α-晶状体蛋白结合为极性分子的通过形成了一个疏水屏障，支持了白内障形成过程中的屏障假说。