title: Accelerated 18O-labeling in urinary proteomics.
abstract: Proteolytic (18)O-labeling of peptides has been studied and optimized in order to improve the labeling efficiency and to accelerate the process without increasing the degree of incomplete labeling. Using peptides generated from tryptic digested bovine serum albumin (BSA) and cytochrome c as model proteins, it was shown that complete labeling was achieved after 2 h at pH 6. To increase the sample throughput in a bottom-up proteomic setup, tryptic digestion of proteins in-solution was replaced with tryptic digestion using immobilized trypsin. As a result, an integrated approach was made possible, where both digestion (pH 8) and (18)O/(16)O-labeling of the resulting peptides (pH 6) were done using immobilized trypsin beads. This simplified the sample handling and reduced the overall reaction time significantly: the setup enabled tryptic digestion and (18)O/(16)O-labeling without sample transfer steps within 3.5 h with average (18)O/(16)O-ratios of 0.96±0.13 in aqueous buffer. The initial results were confirmed with a more complex matrix, by spiking urine with the model proteins, yielding results comparable with the ratios obtained in buffer. Satisfying ratios were also achieved regarding urinary proteins identified in a full scale bottom-up experiment. Average (18)O/(16)O-peptide ratios of 0.83±0.13 and 0.91±0.27 indicated good performance in a highly relevant matrix for biomarker discovery.
authors.affiliation: Department of Pharmaceutical Chemistry, School of Pharmacy, University of Oslo, P.O. Box 1068 Blindern, NO-0316 Oslo, Norway.
authors.forename: Håvard
authors.initials: H
authors.lastname: Loftheim
authors.forename: Anders
authors.initials: A
authors.lastname: Asberg
authors.forename: Léon
authors.initials: L
authors.lastname: Reubsaet
mesh_terms: D000818:Animals; D002417:Cattle; D006801:Humans; D007553:Isotope Labeling / Q000379:methods*; D010103:Oxygen Isotopes / Q000032:analysis*; D010455:Peptides / Q000652:urine; D040901:Proteomics; D012710:Serum Albumin, Bovine / Q000032:analysis; D014556:Urine / Q000737:chemistry*
chemical_list: D010103:Oxygen Isotopes; D010455:Peptides; D012710:Serum Albumin, Bovine