title: Spontaneous deamidation and isomerization of Asn108 in prion peptide 106-126 and in full-length prion protein.
abstract: In prion-related encephalopathies, the cellular prion protein (PrP(C)) undergoes a change in conformation to become the scrapie prion protein (PrP(Sc)) which forms infectious deposits in the brain. Conceivably, the conformational transition of PrP(C) to PrP(Sc) might be linked with posttranslational alterations in the covalent structure of a fraction of the PrP molecules. We tested a synthetic peptide corresponding to residues 106-126 of human PrP for the occurrence of spontaneous chemical modifications. The only asparagine residue, Asn108, was deamidated to aspartic acid and isoaspartic acid with a half-life of about 12 days. The same posttranslational modifications were found in recombinant murine full-length protein. On aging, 0.8 mol of isoaspartyl residue per mole of protein was detected by the protein-l-isoaspartyl methyltransferase assay (t(1/2) approximately 30 days). Mass spectrometry and Edman degradation of Lys-C fragments identified Asn108 in the amino-terminal flexible part of the protein to be partially converted to aspartic acid and isoaspartic acid. A second modification was the partial isomerization of Asp226' which is only present in rodents.
authors.affiliation: Biochemisches Institut der Universität Zürich, Winterthurerstrasse 190, Zürich, CH-8057, Switzerland.
authors.forename: E
authors.initials: E
authors.lastname: Sandmeier
authors.forename: P
authors.initials: P
authors.lastname: Hunziker
authors.forename: B
authors.initials: B
authors.lastname: Kunz
authors.forename: R
authors.initials: R
authors.lastname: Sack
authors.forename: P
authors.initials: P
authors.lastname: Christen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001216:Asparagine / Q000737:chemistry*; D001224:Aspartic Acid / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D006224:Cricetinae; D006801:Humans; D007536:Isomerism; D007700:Kinetics; D013058:Mass Spectrometry; D008666:Metalloendopeptidases / Q000378:metabolism; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry*; D010449:Peptide Mapping; D018621:PrPC Proteins / Q000737:chemistry; D018620:PrPSc Proteins / Q000737:chemistry; D011328:Prions / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D026601:Protein D-Aspartate-L-Isoaspartate Methyltransferase; D011496:Protein Methyltransferases / Q000378:metabolism; D014357:Trypsin / Q000378:metabolism
chemical_list: D010446:Peptide Fragments; D018621:PrPC Proteins; D018620:PrPSc Proteins; D011328:Prions; D001224:Aspartic Acid; D001216:Asparagine; D011496:Protein Methyltransferases; D026601:Protein D-Aspartate-L-Isoaspartate Methyltransferase; D014357:Trypsin; D008666:Metalloendopeptidases; C039830:peptidyl-Lys metalloendopeptidase