The Palladium(II) Complex of A β4-16 as Suitable Model for Structural Studies of Biorelevant Copper(II) Complexes of N-Truncated Beta-Amyloids

Int J Mol Sci. 2020 Dec 2;21(23):9200. doi: 10.3390/ijms21239200.


The Aβ4-42 peptide is a major beta-amyloid species in the human brain, forming toxic aggregates related to Alzheimer's Disease. It also strongly chelates Cu(II) at the N-terminal Phe-Arg-His ATCUN motif, as demonstrated in Aβ4-16 and Aβ4-9 model peptides. The resulting complex resists ROS generation and exchange processes and may help protect synapses from copper-related oxidative damage. Structural characterization of Cu(II)Aβ4-x complexes by NMR would help elucidate their biological function, but is precluded by Cu(II) paramagneticism. Instead we used an isostructural diamagnetic Pd(II)-Aβ4-16 complex as a model. To avoid a kinetic trapping of Pd(II) in an inappropriate transient structure, we designed an appropriate pH-dependent synthetic procedure for ATCUN Pd(II)Aβ4-16, controlled by CD, fluorescence and ESI-MS. Its assignments and structure at pH 6.5 were obtained by TOCSY, NOESY, ROESY, 1H-13C HSQC and 1H-15N HSQC NMR experiments, for natural abundance 13C and 15N isotopes, aided by corresponding experiments for Pd(II)-Phe-Arg-His. The square-planar Pd(II)-ATCUN coordination was confirmed, with the rest of the peptide mostly unstructured. The diffusion rates of Aβ4-16, Pd(II)-Aβ4-16 and their mixture determined using PGSE-NMR experiment suggested that the Pd(II) complex forms a supramolecular assembly with the apopeptide. These results confirm that Pd(II) substitution enables NMR studies of structural aspects of Cu(II)-Aβ complexes.

Keywords: 13C relaxation; ATCUN motif; Alzheimer’s disease; Aβ peptide; NMR spectroscopy; Palladium(II).

MeSH terms

  • Amino Acid Motifs
  • Amyloid beta-Peptides / chemistry*
  • Amyloid beta-Peptides / metabolism
  • Cations / chemistry*
  • Coordination Complexes / chemistry*
  • Coordination Complexes / metabolism
  • Copper / chemistry*
  • Humans
  • Magnetic Resonance Spectroscopy
  • Models, Molecular
  • Models, Theoretical
  • Molecular Conformation
  • Palladium / chemistry*
  • Palladium / metabolism
  • Solutions
  • Structure-Activity Relationship


  • Amyloid beta-Peptides
  • Cations
  • Coordination Complexes
  • Solutions
  • Palladium
  • Copper