title: New experimental evidence for in-chain amino acid racemization of serine in a model peptide.
abstract: The facile racemization of protein-bound amino acids plays an important role in the aging and pathologies of living tissues, and it can be exploited for protein geochronological studies in subfossil biominerals. However, the in-chain degradation pathways of amino acids are complex and difficult to elucidate. Serine has proven to be particularly elusive, and its ability to racemize as a peptide-bound residue (like asparagine and aspartic acid) has not been demonstrated. This study investigates the patterns of degradation of a model peptide (WNSVWAW) at elevated temperatures, quantifying the extent of racemization and peptide bond hydrolysis using reverse-phase high-performance liquid chromatography (RP-HPLC) and tracking the presence of degradation products by MALDI-MS. We provide direct evidence that, under these experimental conditions, both serine and asparagine are able to undergo racemization as internally bound residues, which shows their potential for initiating protein breakdown and provides an explanation for the presence of d-enantiomers in living mammalian tissues.
authors.affiliation: BioArCh, Department of Archaeology, University of York, York YO10 5DD, United Kingdom. beatrice.demarchi@york.ac.uk
authors.forename: Beatrice
authors.initials: B
authors.lastname: Demarchi
authors.forename: Matthew
authors.initials: M
authors.lastname: Collins
authors.forename: Ed
authors.initials: E
authors.lastname: Bergström
authors.forename: Adam
authors.initials: A
authors.lastname: Dowle
authors.forename: Kirsty
authors.initials: K
authors.lastname: Penkman
authors.forename: Jane
authors.initials: J
authors.lastname: Thomas-Oates
authors.forename: Julie
authors.initials: J
authors.lastname: Wilson
mesh_terms: D000596:Amino Acids / Q000737:chemistry / Q000235:genetics; D000818:Animals; D004527:Egg Proteins / Q000737:chemistry* / Q000235:genetics; D010446:Peptide Fragments / Q000737:chemistry* / Q000235:genetics; D017433:Protein Structure, Secondary; D012694:Serine / Q000737:chemistry* / Q000235:genetics; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D013237:Stereoisomerism; D020310:Struthioniformes
chemical_list: D000596:Amino Acids; D004527:Egg Proteins; D010446:Peptide Fragments; C015753:chorion proteins; D012694:Serine