title: Mass spectrometry of laser-initiated carbene reactions for protein topographic analysis.
abstract: We report a protein labeling method using nonselective carbene reactions of sufficiently high efficiency to permit detection by mass spectrometric methods. The approach uses a diazirine-modified amino acid (l-2-amino-4,4'-azipentanoic acid, "photoleucine") as a label source, which is converted to a highly reactive carbene by pulsed laser photolysis at 355 nm. Labeling of standard proteins and peptides (CaM, Mb, M13) was achieved with yields up to 390-fold higher than previous studies using methylene. Carbene labeling is sensitive to changes in protein topography brought about by conformational change and ligand binding. The modification of apo-CaM was 45 ± 7% higher than that of holo-CaM. Modification of the CaM-M13 complex reflected a 39 ± 1% reduction in labeling for bound holo-CaM relative to free holo-CaM. Labeling yield is independent of protein concentration over approximately 2 orders of magnitude but is weakly dependent on the presence of other chromophores in a photon-limited apparatus. The current configuration required 2 min of irradiation for full reagent conversion; however, it is shown that comparable yields can be achieved with a single high-energy laser pulse (>100 mJ/pulse, <10 ns), offering a labeling method with high temporal resolution. We suggest a mechanism of labeling governed by limited carbene diffusion and the protein surface activity of the diazirine precursor. This surface activity is speculated to return a measure of selectivity relative to methylene labeling, which ultimately may be tunable.
authors.affiliation: Department of Chemistry, University of Calgary, Calgary, Alberta, T2N 1N4, Canada.
authors.forename: Chanelle C
authors.initials: CC
authors.lastname: Jumper
authors.forename: David C
authors.initials: DC
authors.lastname: Schriemer
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D002147:Calmodulin / Q000032:analysis*; D003978:Diazomethane / Q000737:chemistry; D007834:Lasers; D013058:Mass Spectrometry; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D018482:Muscle, Skeletal / Q000737:chemistry; D009211:Myoglobin / Q000032:analysis*; D009219:Myosin-Light-Chain Kinase / Q000032:analysis* / Q000378:metabolism; D010782:Photolysis
chemical_list: D000596:Amino Acids; D002147:Calmodulin; D009211:Myoglobin; C030011:carbene; D003978:Diazomethane; D009219:Myosin-Light-Chain Kinase; D008697:Methane