Cu(II)‐Binding N‐Terminal Sequences of Human Proteins

Abstract

Proteins anchor copper(II) ions mainly by imidazole from histidine residues located in different positions in the primary protein structures. However, the motifs with histidine in the first three N‐terminal positions (His1, His2, and His3) show unique Cu(II)‐binding properties, such as availability from the surface of the protein, high flexibility, and high Cu(II) exchangeability with other ligands. It makes such sequences beneficial for the fast exchange of Cu(II) between ligands. Furthermore, sequences with His1 and His2, thus, non‐saturating the Cu(II) coordination sphere, are redox‐active and may play a role in Cu(II) reduction to Cu(I). All human protein sequences deposited in UniProt Knowledgebase were browsed for those containing His1, His2, or His3. Proteolytically modified sequences (with the removal of a propeptide or Met residue) were taken for the analysis. Finally, the sequences were sorted out according to the subcellular localization of the proteins to match the respective sequences with the probability of interaction with divalent copper.

How very small changes in the peptide sequence of β-amyloids influence their redox properties. Electrochemical studies of Aβ(11-16) and pAβ(11-16) in two different electrolytes.

“…Because phosphate anions may influence the Cu(II)-peptide species, the latter buffer better reflects the conditions in the human body. [12,25] Here, the redox behaviour of Cu(II) complexes with Aβ(11-16) (peptide sequence: EVHHQKam) and its pyroglutamate counterpart pAβ (11)(12)(13)(14)(15)(16) (sequence pEVHHQK-am) was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in two kinds of solutions: 4 mM HNO3/96 mM KNO3 and 0.1 M phosphate buffer. Aβ (11)(12)(13)(14)(15)(16) belongs to the ATCUN peptide family, and therefore, the Cu(II) ion is bonded via four nitrogens by the EVH sequence (creating 4N complexes) in a square-planar geometry.…”

Phosphorylation Impacts Cu(II) Binding by ATCUN Motifs

“…More than 100 human extracellular proteins and peptides contain an ATCUN motif, 1 which has an amino acid sequence Xaa-Zaa-His, where Xaa is any amino acid residue with a free N-terminal amine, and Zaa is any amino acid residue except proline. Human histatin-1 and human serum albumin (HSA) contain this motif–Asp-Ser-His and Asp-Ala-His, respectively.…”

“…Based on the recent analysis of N-terminal sequences in human proteins, 1 the selection of human proteins with the ATCUN motif and serine or threonine residue within the first five positions was performed and presented in Table S1 . The threonine residue was added to this analysis as its phosphorylation probably shows the same impact on Cu(II) binding as serine modification.…”

“…It sums up to 72 proteins localized in relatively oxidizing compartments, thus, with a higher probability to meet divalent copper ions. 1 Interestingly, more than 100 other proteins are localized in compartments with a more reducing state ( Table S1 ), such as cytoplasm, nucleus, or mitochondrion. 1 The binding of Cu(II) by those proteins is questionable (because intracellularly Cu(I) is more prevalent than Cu(II)) but cannot be excluded that may occur transiently or in pathological states.…”

“… 1 Interestingly, more than 100 other proteins are localized in compartments with a more reducing state ( Table S1 ), such as cytoplasm, nucleus, or mitochondrion. 1 The binding of Cu(II) by those proteins is questionable (because intracellularly Cu(I) is more prevalent than Cu(II)) but cannot be excluded that may occur transiently or in pathological states. The frequency of Ser or Thr in the sequence position 1, 2, 4, or 5 throughout the whole selection (223 proteins, Table S1 ) is relatively uniform with a slight prevalence of serine residues ( Figure S7 ).…”