Peta-Gaye G. Burnett

New flaxseed orbitides: Detection, sequencing, and 15N incorporation

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 15N‐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.

Rapid reversed-phase liquid chromatography separation of cyclolinopeptides with monolithic and microparticulate columns.

Three monolithic C(18)-bonded silica gel columns i.e. Chromolith SpeedROD (CSR), Chromolith Performance (CP), and Chromolith High Resolution (CHR), MerckKGaA Darmstadt, Germany and two particle-based columns i.e. ZORBAX Eclipse XDB-C(18) (ZEX), Agilent and POROS R1/20 (POR), Applied Biosystems were compared for their performance in separating a mixture of flaxseed cyclolinopeptides (CLs). Gradient mobile phases of acetonitrile and water were optimized for each column. The performance of CHR column in profiling CL standards, measured as the resolution of individual CL, selectivity, and peak asymmetry exceeded the performance of traditional particle-packed columns and the other monolithic columns. The profiling of CLs in aqueous methanolic flaxseed extract was optimized for high-throughput analysis. A total analysis time of 1.5 min at a flow rate of 3.0mLmin(-1) was achieved on a CSR column. Injection of over 2000 methanol extracts of flaxseed on a CSR column had no impact on backpressure or resolution of a standard CL mixture.

Glycine-containing flaxseed orbitides.

Five new orbitides, cyclolinopeptides 21-25, were identified in flaxseed oil (Linum usitatissimum) extracts. Their HPLC-ESIMS quasimolecular ion peaks at m/z 1097.7 (21), 1115.6 (22), 1131.6 (23), 1018.6 (24), and 1034.6 (25) [M + H](+) corresponded to the molecular formulae C59H89N10O10, C58H87N10O10S, C58H87N10O11S, C53H80N9O9S, and C53H80N9O10S, respectively. Their structures were elucidated by extensive HPLC-ESIMS/MS analyses, and their presence was confirmed by precursor proteins identified in flax genomic DNA sequence data. The amino acid sequences of these orbitides were confirmed as [1-10-NαC]-GILVPPFFLI, [1-10-NαC]-GMLIPPFFVI, [1-10-NαC]-GOLIPPFFVI, [1-9-NαC]-GMLVFPLFI, and [1-9-NαC]-GOLVFPLFI for cyclolinopeptides 21-25, respectively. Previously reported orbitides, [1-9-NαC]-ILVPPFFLI (1), [1-9-NαC]-MLIPPFFVI (2), [1-9-NαC]-OLIPPFFVI (3), [1-8-NαC]-MLVFPLFI (7), and [1-8-NαC]-OLVFPLFI (8), were also present in flaxseed oil. The precursors of orbitides 21, 22, and 24 also produced orbitides 1, 2, and 7 by alternative cyclization. Cyclolinopeptides 3, 8, 23, and 25 contain MetO (O) and are not directly encoded, but are products of post-translational modification of the Met present in 2, 7, 22, and 24, respectively. Sufficient cyclolinopeptide 23 was isolated for characterization via 1D ((1)H and (13)C) and 2D (NOESY and HMBC) NMR spectroscopy. These compounds have been named as cyclolinopeptides U, V, W, X, and Y for 21, 22, 23, 24, and 25, respectively.

Cyclo-linopeptide K butanol disolvate monohydrate.

The title compound, C56H83N9O11S·2C4H10O·H2O, is a butanol–water solvate of the cyclolinopeptide cyclo(Metsulfone1-Leu2–Ile3–Pro4–Pro5–Phe6–Phe7–Val8–Ile9) (henceforth referred to as CLP-K) which was isolated from flax oil. All the amino acid residues are in an l configuration based on the CORN rule. The cyclic nonapeptide exhibits eight trans peptide bonds and one cis peptide bond observed between the two proline residues. The conformation is stabilized by an α- and a β-turn, each containing an N—H⋯O hydrogen bond between the carbonyl group O atom of the first residue and the amide group H atom of the fourth (α-turn) and the third residue (β-turn), repectively. In the crystal, the components of the structure are linked by intermolecular N—H⋯O and O—H⋯O hydrogen bonds into a two-dimensional network parallel to (001). The –C(H2)OH group of one of the butanol solvent molecules is disordered over two sets of sites with refined occupancies of 0.863 (4) and 0.137 (4).

Simulated moving bed purification of flaxseed oil orbitides: unprecedented separation of cyclolinopeptides C and E.

The purification and enrichment of most natural products with potential pharmaceutical applications has been performed mainly employing conventional batch-mode chromatographic processes. There is a growing interest in use of simulated moving bed (SMB) chromatography for natural product enrichment as this method enables conservation of mobile phase, while increasing productivity of chromatography medium. SMB increases yield while decreasing cost. Cyclolinopeptides C ([1-9-NaC],[1-MetO]-CLB, 3) and E ([1-8-NaC],[1-MetO]-CLE, 8) were extracted as a mixture from flaxseed oil and then enriched using a three-zone simulated moving bed. The current research extends the SMB technology to enrichment of cyclolinopeptides (CLs), a group of biologically active hydrophobic cyclic peptides that occur in flaxseed oil. Of interest are [1-9-NaC],[1-MetO]-CLB (3) and [1-8-NaC],[1-MetO]-CLE (8) that provide synthetic scaffolds for modified CLs. The influence of flow rate (feed, desorbent, and extract) on the separation of [1-9-NaC],[1-MetO]-CLB (3) and [1-8-NaC],[1-MetO]-CLE (8) was investigated.

Cyclo­linopeptide B methanol tris­olvate

The title compound, C56H83N9O9S·3CH3OH, is a methanol trisolvate of the cyclolinopeptide cyclo(Met1—Leu2—Ile3—Pro4—Pro5—Phe6—Phe7—Val8—Ile9) (henceforth referred to as CLP-B), which was isolated from flaxseed oil. All the amino acid residues are in an l-configuration based on the CORN rule. The cyclic nonapeptide exhibits eight trans peptide bonds and one cis peptide bond observed between the two proline residues. The conformation is stabilized by an α-turn and two consecutive β-turns each containing a N—H⋯O hydrogen bond between the carbonyl group O atom of the first residue and the amide group H atom of the fourth (α-turn) or the third residue (β-turns), repectively. In the crystal, the components of the structure are linked by N—H⋯O and O—H⋯O hydrogen bonds into chains parallel to the a axis.

Self-assembled fibrillar networks comprised of a naturally-occurring cyclic peptide—LOB3

To the best of our knowledge, this is the first report of a self-assembling orbitide that is capable of forming 1D nano-fibers and ultimately 3D molecular gel networks. LOB3 (a.k.a. cyclolinopeptide A), extracted from Linum usitatissimum L. (flaxseed), forms molecular gels in acetonitrile. LOB3 molecular gels, illustrate that cyclic peptides may be comprised of more complex amino acid sequences than have been currently reported. It appears that cyclization, to form orbitides, imparts conformational aspects to the molecule facilitating self-organization into crystalline nano-fibers. These nanoscale fibers, ∼300 nm in diameter and >100 μm in length, aggregate into bundles of fibers which may exceed micron dimensions. Within the nano-fibers, the orbitides adapt an antiparallel β-sheet-like conformation with high molecular periodicity, as illustrated by CD and XRD.

Novel flax orbitide derived from genetic deletion

BackgroundFlaxseed orbitides are homodetic plant cyclic peptides arising from ribosomal synthesis and post-translation modification (N to C cyclization), and lacking cysteine double bonds (Nat Prod Rep 30:108-160, 2013). Screening for orbitide composition was conducted on the flax core collection (FCC) grown at both Saskatoon, Saskatchewan and Morden, Manitoba over three growing seasons (2009-2011). Two flax (Linum usitatissimum L.) accessions ‘Hollandia’ (CN 98056) and ‘Z 11637’ (CN 98150) produce neither [1−9-NαC]-linusorb B2 (3) nor [1−9-NαC]-linusorb B3 (1). Mass spectrometry was used to identify novel compounds and elucidate their structure. NMR spectroscopy was used to corroborate structural information.ResultsExperimental findings indicated that these accessions produce a novel orbitide, identified in three oxidation states having quasimolecular ion peaks at m/z 1072.6 (18), 1088.6 (19), and 1104.6 (20) [M + H]+ corresponding to molecular formulae C57H86N9O9S, C57H86N9O10S, and C57H86N9O11S, respectively. The structure of 19 was confirmed unequivocally as [1−9-NαC]-OLIPPFFLI. PCR amplification and sequencing of the gene coding for 18, using primers developed for 3 and 1, identified the putative linear precursor protein of 18 as being comprised of the first three amino acid residues of 3 (MLI), four conserved amino acid residues of 3 and/or 1 (PPFF), and the last two residues of 1 (LI).ConclusionComparison of gene sequencing data revealed that a 117 base pair deletion had occurred that resulted in truncation of both 3 and 1 to produce a sequence encoding for the novel orbitide precursor of 18. This observation suggests that repeat units of flax orbitide genes are conserved and suggests a novel mechanism for evolution of orbitide gene diversity. Orbitides 19 and 20 contain MetO and MetO2, respectively, and are not directly encoded, but are products of post-translation modification of Met present in 18 ([1−9-NαC]-MLIPPFFLI).