Fragment length influences affinity for Cu2+ and Ni2+ binding to His96 or His111 of the prion protein and spectroscopic evidence for a multiple histidine binding only at low pH.
The prion protein (PrP) is a Cu2+-binding cell-surface glycoprotein. Using various PrP fragments and spectroscopic techniques, we show that two Cu2+ ions bind to a region between residues 90 and 126. This region incorporates the neurotoxic portion of PrP, vital for prion propagation in transmissible spongiform encephalopathies. Pentapeptides PrP-(92-96) and PrP-(107-111) represent the minimum motif for Cu2+ binding to the PrP-(90-126) fragment. Consequently, we were surprised that the appearance of the visible CD spectra for two fragments of PrP, residues 90-126 and 91-115, are very different. We have shown that these differences do not arise from a change in the co-ordination geometry within the two fragments; rather, there is a change in the relative preference for the two binding sites centred at His111 and His96. These preferences are metal-, pH- and chain-length dependent. CD indicates that Cu2+ initially fills the site at His111 within the PrP-(90-126) fragment. The pH-dependence of the Cu2+ co-ordination is studied using EPR, visible CD and absorption spectroscopy. We present evidence that, at low pH (5.5) and sub-stoichiometric amounts of Cu2+, a multiple histidine complex forms, but, at neutral pH, Cu2+ binds to individual histidine residues. We have shown that changes in pH and levels of extracellular Cu2+ will affect the co-ordination mode, which has implications for the affinity, folding and redox properties of Cu-PrP.
Klewpatinond
Mark
M
School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, U.K.
Viles
John H
JH
D000595:Amino Acid Sequence; D002942:Circular Dichroism; D003300:Copper / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D006639:Histidine / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009532:Nickel / Q000378:metabolism*; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011328:Prions / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding
D010446:Peptide Fragments; D011328:Prions; D006639:Histidine; D003300:Copper; D009532:Nickel