Copper binding to the octarepeats of the prion protein. Affinity, specificity, folding, and cooperativity: insights from circular dichroism.
The prion protein (PrP) is a Cu(2+) binding cell surface glycoprotein. There is increasing evidence that PrP functions as a copper transporter. In addition, strains of prion disease have been linked with copper binding. We present here CD spectroscopic studies of Cu(2+) binding to various fragments of the octarepeat region of the prion protein. We show that glycine and l-histidine will successfully compete for all Cu(2+) ions bound to the PrP octapeptide region, suggesting Cu(2+) coordinates with a lower affinity for PrP than the fm dissociation constant reported previously. We show that each of the octarepeats do not form an isolated Cu(2+) binding motif but fold up cooperatively within multiple repeats. In addition to the coordinating histidine side chain residues, we show that the glycine residues and the proline within each octarepeat are also necessary to maintain the coordination geometry. The highly conserved octarepeat region in mammals is a hexarepeat in birds that also binds copper but with different coordination geometry. Finally, in contrast to other reports, we show that Mn(2+) does not bind to the octarepeat region of PrP.
Garnett
Anthony P
AP
School of Biological Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, United Kingdom.
Viles
John H
JH
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D002942:Circular Dichroism; D003300:Copper / Q000737:chemistry / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005998:Glycine / Q000737:chemistry; D006639:Histidine / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008345:Manganese / Q000737:chemistry; D008969:Molecular Sequence Data; D009154:Mutation; D010452:Peptide Biosynthesis; D018621:PrPC Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017510:Protein Folding; D017386:Sequence Homology, Amino Acid; D013053:Spectrophotometry; D013379:Substrate Specificity; D014466:Ultraviolet Rays
D018621:PrPC Proteins; D008345:Manganese; D006639:Histidine; D003300:Copper; D005998:Glycine