BPS2025 - Interaction of α-crystallin with a model of bovine lens-lipid membrane is modulated by temperature and membrane cholesterol

α-Crystallin binding to the lens membrane increases with age and cataracts. Elevated temperatures have also been linked to the development of cataracts, and cholesterol (Chol) content in lens membranes increases with aging. However, how temperature influences α-crystallin membrane binding, and the role of membrane cholesterol in such binding is unclear; this study used the electron paramagnetic resonance (EPR) spin-labeling method to study the effects of temperature and Chol on α-crystallin binding to the (Chol)/model of bovine lens-lipid (MBLL) membranes with Chol/MBLL mixing ratio of 0, 0.3, and 1.5. Chol/MBLL membranes were incubated with α-crystallin at various temperatures of 30°C, 37°C, 45°C, and 52°C, followed by EPR measurements at 37°C. Our results show that for the Chol/MBLL mixing ratio of 0 and 0.3, the maximum percentage of membrane surface occupied (MMSO) by α-crystallin and binding affinity (Ka) of α-crystallin to Chol/MBLL membranes followed the trends: MMSO (37°C) > MMSO (45°C) ≈ MMSO (52°C) > MMSO (30°C) and Ka (37°C) > Ka (30°C) > Ka (45°C) ≈ Ka (52°C) indicating that temperature modulates the amount of α-crystallin bound on the membrane surface and the Ka of α-crystallin to membranes. However, at all temperatures investigated, MMSO by α-crystallin and Ka of α-crystallin to Chol/MBLL membrane are zero at Chol/MBLL mixing ratio of 1.5, indicating high Chol and cholesterol bilayer domains completely inhibit binding of α-crystallin to membranes independently of temperature. Our results show that incubation temperatures modulate the mobility and hydrophobicity near the headgroup regions of Chol/MBLL membranes at a mixing ratio of 0 and 0.3 with α-crystallin binding. In contrast, no significant changes in mobility and hydrophobicity were observed at a mixing ratio of 1.5.