Key roles of Arg5, Tyr10 and His residues in Aβ-heme peroxidase: Relevance to Alzheimer's disease

Recent reports show that heme binds to amyloid β-peptide (Aβ) in the brain of Alzheimer's disease (AD) patients and forms Aβ-heme complexes, thus leading a pathological feature of AD. However, the important biological relevance to AD etiology, resulting from human Aβ-heme peroxidase formation, was not well characterized. In this study, we used wild-type and mutated human Aβ1-16 peptides and investigated their Aβ-heme peroxidase activities. Our results indicated that both histidine residues (His13, His14) in Aβ1-16 and free histidine enhanced the peroxidase activity of heme, hence His residues were essential in peroxidase activity of Aβ-heme complexes. Moreover, Arg5 was found to be the key residue in making the Aβ1-16-heme complex as a peroxidase. Under oxidative and nitrative stress conditions, the Aβ1-16-heme complexes caused oxidation and nitration of the Aβ Tyr10 residue through promoting peroxidase-like reactions. Therefore, these residues (Arg5, Tyr10 and His) were pivotal in human Aβ-heme peroxidase activity. However, three of these residues (Arg5, Tyr10 and His13) identified in this study are all absent in rodents, where rodent Aβ-heme complex lacks peroxidase activity and it does not show AD, implicating the novel significance of these residues as well as human Aβ-heme peroxidase in the pathology of AD.