Copper-dependent inhibition of cytochrome c oxidase by Abeta(1-42) requires reduced methionine at residue 35 of the Abeta peptide.
By altering key amino acid residues of the Alzheimer's disease-associated amyloid-beta peptide, we investigated the mechanism through which amyloid-beta inhibits cytochrome c oxidase (EC 1.9.3.1). Native amyloid-beta inhibited cytochrome oxidase by up to 65%, and the level of inhibition was determined by the period of amyloid-beta ageing before the cytochrome oxidase assay. Substituting tyrosine-10 with alanine did not affect maximal enzyme inhibition, but the altered peptide required a longer period of ageing. By contrast, oxidizing the sulfur of methionine-35 to a sulfoxide, or substituting methionine-35 with valine, completely abrogated the peptide's inhibitory potential towards cytochrome oxidase. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that the loss of inhibitory potential towards cytochrome oxidase with the methionine-35-altered peptides did not correlate with a substantially different distribution of amyloid-beta oligomeric species. Although the amyloid-beta-mediated inhibition of cytochrome oxidase was completely dependent on the presence of divalent Cu2+, it was not supported by monovalent Cu+, and experiments with catalase and H2O2 indicated that the mechanism of cytochrome oxidase inhibition does not involve amyloid-beta-mediated H2O2 production. We propose that amyloid-beta-mediated inhibition of cytochrome oxidase is dependent on the peptide's capacity to bind, then reduce Cu2+, and that it may involve the formation of a redox active amyloid-beta-methionine radical.
Crouch
Peter J
PJ
Centre for Neuroscience, The University of Melbourne, Victoria, Australia.
Barnham
Kevin J
KJ
Duce
James A
JA
Blake
Rachel E
RE
Masters
Colin L
CL
Trounce
Ian A
IA
D016229:Amyloid beta-Peptides / Q000737:chemistry* / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000502:physiology / Q000648:ultrastructure; D002478:Cells, Cultured; D003300:Copper / Q000494:pharmacology*; D003576:Electron Transport Complex IV / Q000037:antagonists & inhibitors*; D006801:Humans; D008214:Lymphocytes; D008715:Methionine; D051379:Mice; D010446:Peptide Fragments / Q000737:chemistry* / Q000494:pharmacology*; D013367:Submitochondrial Particles / Q000187:drug effects / Q000502:physiology*
D016229:Amyloid beta-Peptides; D010446:Peptide Fragments; C075222:amyloid beta-protein (1-42); D003300:Copper; D008715:Methionine; D003576:Electron Transport Complex IV