Brain S100A5 is a novel calcium-, zinc-, and copper ion-binding protein of the EF-hand superfamily.
S100A5 is a novel member of the EF-hand superfamily of calcium-binding proteins that is poorly characterized at the protein level. Immunohistochemical analysis demonstrates that it is expressed in very restricted regions of the adult brain. Here we characterized the human recombinant S100A5, especially its interaction with Ca(2+), Zn(2+), and Cu(2+). Flow dialysis revealed that the homodimeric S100A5 binds four Ca(2+) ions with strong positive cooperativity and an affinity 20-100-fold higher than the other S100 proteins studied under identical conditions. S100A5 also binds two Zn(2+) ions and four Cu(2+) ions per dimer. Cu(2+) binding strongly impairs the binding of Ca(2+); however, none of these ions change the alpha-helical-rich secondary structure. After covalent labeling of an exposed thiol with 2-(4'-(iodoacetamide)anilino)-naphthalene-6-sulfonic acid, binding of Cu(2+), but not of Ca(2+) or Zn(2+), strongly decreased its fluorescence. In light of the three-dimensional structure of S100 proteins, our data suggest that in each subunit the single Zn(2+) site is located at the opposite side of the EF-hands. The two Cu(2+)-binding sites likely share ligands of the EF-hands. The potential role of S100A5 in copper homeostasis is discussed.
Schäfer
B W
BW
Department of Pediatrics, Division of Clinical Chemistry and Biochemistry, University of Zurich, Steinwiesstrasse 75, CH-8032 Zurich, the Institute of Pharmacology, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
Fritschy
J M
JM
Murmann
P
P
Troxler
H
H
Durussel
I
I
Heizmann
C W
CW
Cox
J A
JA
D000494:Allosteric Regulation; D000818:Animals; D001665:Binding Sites; D001923:Brain Chemistry; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002413:Cations, Divalent / Q000378:metabolism; D018797:Cell Cycle Proteins; D002942:Circular Dichroism; D003300:Copper / Q000378:metabolism*; D019791:Guanidine; D006801:Humans; D007091:Image Processing, Computer-Assisted; D018613:Microscopy, Confocal; D005810:Multigene Family; D009830:Olfactory Bulb / Q000737:chemistry; D010446:Peptide Fragments / Q000378:metabolism; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000378:metabolism; D000075383:S100 Calcium Binding Protein A6; D009418:S100 Proteins / Q000235:genetics / Q000378:metabolism*; D017552:Solitary Nucleus / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D014018:Tissue Distribution; D015032:Zinc / Q000378:metabolism*
D002135:Calcium-Binding Proteins; D002413:Cations, Divalent; D018797:Cell Cycle Proteins; D010446:Peptide Fragments; D011994:Recombinant Proteins; D000075383:S100 Calcium Binding Protein A6; D009418:S100 Proteins; C082355:S100A5 protein, human; C489132:S100a6 protein, rat; C055351:S100A6 protein, human; D003300:Copper; D015032:Zinc; D019791:Guanidine; D002118:Calcium