Al cation induces aggregation of serum proteins

Al cation is known to induce protein fibrillation and causes several neurodegenerative disorders. We report the spectroscopic, thermodynamic analysis and AFM imaging for the Al cation binding process with human serum albumin (HSA), bovine serum albumin (BSA) and milk beta-lactoglobulin (b-LG) in aqueous solution at physiological pH. Hydrophobicity played a major role in Al–protein interactions with more hydrophobic b-LG forming stronger Al–protein complexes. Thermodynamic parameters ΔS, ΔH and ΔG showed Al–protein bindings occur via hydrophobic and H-bonding contacts for b-LG, while van der Waals and H-bonding interactions prevail in HSA and BSA adducts. AFM clearly indicated that aluminum cations are able to force BSA and b-LG into larger or more robust aggregates than HSA, with HSA 4 ± 0.2 (SE, n = 801) proteins per aggregate, for BSA 17 ± 2 (SE, n = 148), and for b-LG 12 ± 3 (SE, n = 151). Thioflavin T test showed no major protein fibrillation in the presence of Al cation. Al complexation induced major alterations of protein conformations with the order of perturbations b-LG > BSA > HSA.