title: New flaxseed orbitides: Detection, sequencing, and (15)N incorporation.
abstract: Three new orbitides (cyclolinopeptides 17, 18, and 19) were identified in flaxseed (Linum usitatissimum L.) extracts without any form of purification. Their structures were elucidated by a combination of (15) N-labeling experiments and extensive tandem mass spectrometry (MS/MS) with electrospray ionization (ESI). Putative linear peptide sequences of the new orbitides were used as the query in the Basic Local Alignment Search Tool (BLAST) searches of flax genome database. These searches returned linear sequences for the putative precursors of cyclolinopeptides 17 and 19 among others. Cyclolinopeptide 18 contains MetO (O) and is not directly encoded, but is a product of post-translation modification of the Met present in 17. The identification of precursor proteins in flax mRNA transcripts and DNA sequences confirmed the occurrence and amino acid sequences of these orbitides as [1-9-NαC]-MLKPFFFWI, [1-9-NαC]-OLKPFFFWI, and [1-9-NαC]-GIPPFWLTL for cyclolinopeptides 17, 18, and 19, respectively.
authors.affiliation: Department of Plant Sciences, College of Agriculture and Bioresources, University of Saskatchewan, Saskatoon, SK, S7N 5A8, Canada.
authors.forename: Denis P
authors.initials: DP
authors.lastname: Okinyo-Owiti
authors.forename: Lester
authors.initials: L
authors.lastname: Young
authors.forename: Peta-Gaye G
authors.initials: PG
authors.lastname: Burnett
authors.forename: Martin J T
authors.initials: MJ
authors.lastname: Reaney
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002851:Chromatography, High Pressure Liquid; D019597:Flax / Q000737:chemistry*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009587:Nitrogen Isotopes; D010456:Peptides, Cyclic / Q000737:chemistry*; D012639:Seeds / Q000737:chemistry*; D020539:Sequence Analysis, Protein; D053719:Tandem Mass Spectrometry
chemical_list: D009587:Nitrogen Isotopes; D010456:Peptides, Cyclic
keywords: cyclic peptides; flax; mass spectrometry; orbitides; sequencing