https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4120975/
J Phys Chem B. 2014 Jul 31; 118(30): 8935–8944.
Published online 2014 Jul 11. doi: 10.1021/jp500767n
ESEEM Analysis of Multi-Histidine Cu(II)-Coordination in Model Complexes, Peptides, and Amyloid-β
We validate the use of ESEEM to predict the number of 14N nuclei coupled to a Cu(II) ion by the use of model complexes and two small peptides with well-known Cu(II) coordination. We apply this method to gain new insight into less explored aspects of Cu(II) coordination in amyloid-β (Aβ). Aβ has two coordination modes of Cu(II) at physiological pH. A controversy has existed regarding the number of histidine residues coordinated to the Cu(II) ion in component II, which is dominant at high pH (∼8.7) values. Importantly, with an excess amount of Zn(II) ions, as is the case in brain tissues affected by Alzheimer’s disease, component II becomes the dominant coordination mode, as Zn(II) selectively substitutes component I bound to Cu(II). We confirm that component II only contains single histidine coordination, using ESEEM and set of model complexes. The ESEEM experiments carried out on systematically 15N-labeled peptides reveal that, in component II, His 13 and His 14 are more favored as equatorial ligands compared to His 6. Revealing molecular level details of subcomponents in metal ion coordination is critical in understanding the role of metal ions in Alzheimer’s disease etiology.
Introduction
Among natural amino acids histidine is one of the strongest metal ion coordinators.
1 Hence, histidine plays an important role in metal ion coordination in proteins and peptides. Histidine is a tridentate ligand, which provides ligands at the imidazole imido nitrogen, the amino nitrogen, and the carboxylate oxygen.
2 The imidazole ring nitrogen of histidine residues often provides the primary coordination site for metal ions.
2Copper is an essential metal ion for biological functions and is found in bound forms in metalloproteins and in low molecular weight complexes to avoid toxicity associated with free copper.
2 Copper-containing proteins often have binding sites with irregular geometries containing one or more histidine ligands.
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