Effect of lipid environment on amyloid fibril formation of human serum amyloid A

Human serum amyloid A (SAA) is a precursor protein of AA amyloidosis and a component of high-density lipoproteins (HDLs), thus it is essential to investigate the amyloid fibril formation of SAA under a lipid environment. We used synthetic fragment peptides corresponding to the N-terminal (residues 1-27) and central (residues 43-63) regions of the SAA molecule, which are known to have amyloidogenic properties. Measurements of tryptophan fluorescence in conjunction with circular dichroism showed that SAA (1-27) peptide binds to neutral and acidic lysophospholipids, whereas SAA (43-63) peptide binds only to acidic lysophospholipids. For both these SAA peptides, binding to lysophospholipids inhibited heparin-induced amyloid-like fibril formation by stabilizing the α-helical structure. However, acidic lysophospholipids implied a possibility to promote fibril formation of SAA (1-27) peptide by themselves. These results suggest that the amyloid fibril formation of SAA may be modulated by altering the lipid head group composition of HDLs during metabolism.