Direct Evidence That All Three Histidine Residues Coordinate to Cu(II) in Amyloid-β1−16

• Published in: Biochemistry (Easton) 2008-09, Vol.47 (35), p.9117-9123
• Main Authors: Shin, Byong-kyu, Saxena, Sunil
• Format: Article
• Language: English
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi801014x

We provide direct evidence that all three histidine residues in amyloid-β1−16 (Aβ1−16) coordinate to Cu(II). In our approach, we generate Aβ1−16 analogues, in each of which a selected histidine residue is isotopically enriched with 15N. Pulsed electron spin resonance (ESR) experiments such as electron spin echo envelope modulation (ESEEM) and hyperfine sublevel correlation (HYSCORE) spectroscopy clearly show that all three histidine imidazole rings at positions 6, 13 and 14 in Aβ1−16 bind to Cu(II). The method employed here does not require either chemical side chain modification or amino acid residue replacement, each of which is traditionally used to determine whether an amino acid residue in a protein binds to a metal ion. We find that the histidine coordination in the Aβ1−16 peptide is independent of the Cu(II)-to-peptide ratio, which is in contrast to the Aβ1−40 peptide. The ESR results also suggest tight binding between the histidine residues and the Cu(II) ion, which is likely the reason for the high binding affinity of the Aβ peptide for Cu(II).