A comparative study on flaxseed lignan biotransformation through resting cell catalysis and microbial fermentation by ß-glucosidase production Lactiplantibacillus plantarum.

BACKGROUND: Flax lignan has attracted much attention because of its potential bioactivities. However, the bioavailability of secoisolariciresinol diglucoside (SDG), the main lignan in flaxseed, depends on the bioconversion by the colon bacteria. Lactic acid bacteria (LAB) with ß-glucosidase activity has found wide application in preparing bioactive aglycone. RESULTS: LAB strains with good ß-glucosidase activity were isolated from fermented tofu. Their bioconversion of flax lignan extract was investigated by resting cell catalysis and microbial fermentation, and the metabolism of SDG by Lactiplantibacillus plantarum C5 following fermentation was characterized by widely targeted metabolomics. Five L. plantarum strains producing ß-glucosidase with broad substrate specificity were isolated and identified, and they all can transform SDG into secoisolariciresinol (SECO). L. plantarum C5 resting cell reached a maximum SDG conversion of 49.19 ± 3.75%, and SECO generation of 21.49 ± 1.32% (0.215 ± 0.013 mm) at an SDG substrate concentration of 1 mM and 0.477 ± 0.003 mm SECO was produced at 4 mm within 24 h. Although sixteen flax lignan metabolites were identified following the fermentation of SDG extract by L. plantarum C5, among them, four were produced following the fermentation: SECO, demethyl-SECO, demethyl-dehydroxy-SECO and isolariciresinol. Moreover, seven lignans increased significantly. CONCLUSION: Fermentation significantly increased the profile and level of flax lignan metabolites, and the resting cell catalysis benefits from higher bioconversion efficiency and more straightforward product separation. Resting cell catalysis and microbial fermentation of flax lignan extract by the isolated ß-glucosidase production L. plantarum could be potentially applied in preparing flax lignan ingredients and fermented flaxseed. © 2024 Society of Chemical Industry.

Mycoproteins and their health-promoting properties: Fusarium species and beyond.

Filamentous fungal mycoproteins have gained increasing attention as sustainable alternatives to animal and plant-based proteins. This comprehensive review summarizes the nutritional characteristics, toxicological aspects, and health-promoting effects of mycoproteins, focusing on those derived from filamentous fungi, notably Fusarium venenatum. Mycoproteins are characterized by their high protein content, and they have a superior essential amino acid profile compared to soybeans indicating excellent protein quality and benefits for human nutrition. Additionally, mycoproteins offer enhanced digestibility, further highlighting their suitability as a protein source. Furthermore, mycoproteins are rich in dietary fibers, which have been associated with health benefits, including protection against metabolic diseases. Moreover, their fatty acids profile, with significant proportions of polyunsaturated fatty acids and absence of cholesterol, distinguishes them from animal-derived proteins. In conclusion, the future of mycoproteins as a health-promoting protein alternative and the development of functional foods relies on several key aspects. These include improving the acceptance of mycoproteins, conducting further research into their mechanisms of action, addressing consumer preferences and perceptions, and ensuring safety and regulatory compliance. To fully unlock the potential of mycoproteins and meet the evolving needs of a health-conscious society, continuous interdisciplinary research, collaboration among stakeholders, and proactive engagement with consumers will be vital.

Electrostatic field as an emergent technology in refining crude oils: a review.

Vegetable oils and fatty acid esters (FAEs) are commonly used in various industrial and commercial applications. However, the presence of contaminants in these oils can severely affect their functionality and suitability. Conventional refining techniques for vegetable oils typically involve degumming, neutralization, bleaching and deodorization. Meanwhile, refining of FAEs often utilize wet or dry washing processes. These are often resource-intensive, producing substantial waste products, causing neutral oil loss, and can also result in the loss of micronutrients. To address these challenges, researchers have explored the use of nano-adsorbents and electrostatic field (E-field) technologies as alternatives in purifying industrial dielectric oils by removing polar particles and contaminants. Nano-adsorbents demonstrated increased efficiency in removing polar contamination while minimizing neutral oil loss. However, removal of these spent adsorbents can be challenging due to their nano-size, and physicochemical properties. The use of these materials combined with E-field technologies offers a novel and sustainable solution for removing spent nano-adsorbents and contaminants. This review provides an overview of current traditional and novel refining technologies for vegetable oils and FAEs, including their associated limitations. Compared to conventional methods, E-field treatment offers several advantages, making it an attractive alternative to conventional approaches in food processing and oil refining.

Availability of bioactive flax lignan from foods and supplements.

Hyperlipidemia, high levels of blood lipids including cholesterol and triglycerides, is a major risk factor for cardiovascular disease. Traditional treatments of hyperlipidemia often include lifestyle changes and pharmacotherapy. Recently, flaxseed has been approved as a nutrient that lowers blood lipids. Several metabolites of flaxseed lignan secoisolariciresinol diglucoside (SDG), have been identified that reduce blood lipids. SDG is present in flaxseed hull as an ester-linked copolymer with 3-hydroxy-3-methylglutaric acid (HMGA). However, purification processes involved in hydrolysis of the copolymer and enriching SDG are often expensive. The natural copolymer of SDG with HMGA (SDG polymer) is a source of bioactive compounds useful in prophylaxis of hypercholesterolemia. After consumption of the lignan copolymer, SDG and HMGA are released in the stomach and small intestines. SDG is metabolized to secoisolariciresinol, enterolactone and enterodiol, the bioactive forms of mammalian lignans. These metabolites are then distributed throughout the body where they accumulate in the liver, kidney, skin, other tissues, and organs. Successively, these metabolites reduce blood lipids including cholesterol, triglycerides, low density lipoprotein cholesterol, and lipid peroxidation products. In this review, the metabolism and efficacies of flaxseed-derived enriched SDG and SDG polymer will be discussed.

A Metabolomics and Big Data Approach to Cannabis Authenticity (Authentomics).

With the increasing accessibility of cannabis (Cannabis sativa L., also known as marijuana and hemp), its products are being developed as extracts for both recreational and therapeutic use. This has led to increased scrutiny by regulatory bodies, who aim to understand and regulate the complex chemistry of these products to ensure their safety and efficacy. Regulators use targeted analyses to track the concentration of key bioactive metabolites and potentially harmful contaminants, such as metals and other impurities. However, the metabolic complexity of cannabis metabolic pathways requires a more comprehensive approach. A non-targeted metabolomic analysis of cannabis products is necessary to generate data that can be used to determine their authenticity and efficacy. An authentomics approach, which involves combining the non-targeted analysis of new samples with big data comparisons to authenticated historic datasets, provides a robust method for verifying the quality of cannabis products. To meet International Organization for Standardization (ISO) standards, it is necessary to implement the authentomics platform technology and build an integrated database of cannabis analytical results. This study is the first to review the topic of the authentomics of cannabis and its potential to meet ISO standards.

The flax genome reveals orbitide diversity.

BACKGROUND: Ribosomally-synthesized cyclic peptides are widely found in plants and exhibit useful bioactivities for humans. The identification of cyclic peptide sequences and their precursor proteins is facilitated by the growing number of sequenced genomes. While previous research largely focused on the chemical diversity of these peptides across various species, there is little attention to a broader range of potential peptides that are not chemically identified. RESULTS: A pioneering study was initiated to explore the genetic diversity of linusorbs, a group of cyclic peptides uniquely occurring in cultivated flax (Linum usitatissimum). Phylogenetic analysis clustered the 5 known linusorb precursor proteins into two clades and one singleton. Preliminary tBLASTn search of the published flax genome using the whole protein sequence as query could only retrieve its homologues within the same clade. This limitation was overcome using a profile-based mining strategy. After genome reannotation, a hidden Markov Model (HMM)-based approach identified 58 repeats homologous to the linusorb-embedded repeats in 8 novel proteins, implying that they share common ancestry with the linusorb-embedded repeats. Subsequently, we developed a customized profile composed of a random linusorb-like domain (LLD) flanked by 5 conserved sites and used it for string search of the proteome, which extracted 281 LLD-containing repeats (LLDRs) in 25 proteins. Comparative analysis of different repeat categories suggested that the 5 conserved flanking sites among the non-homologous repeats have undergone convergent evolution driven by functional selection. CONCLUSIONS: The profile-based mining approach is suitable for analyzing repetitive sequences. The 25 LLDR proteins identified herein represent the potential diversity of cyclic peptides within the flax genome and lay a foundation for further studies on the functions and evolution of these protein tandem repeats.

Health benefits of flaxseed and its peptides (linusorbs).

Flaxseed (Linum usitatissimum L.) has been associated with numerous health benefits. The flax plant synthesizes an array of biologically active compounds including peptides or linusorbs (LOs, a.k.a., cyclolinopeptides), lignans, soluble dietary fiber and omega-3 fatty acids. The LOs arise from post-translational modification of four or more ribosome-derived precursors. These compounds exhibit an array of biological activities, including suppression of T-cell proliferation, excessive inflammation, and osteoclast replication as well as induction of apoptosis in some cancer cell lines. The mechanisms of LO action are only now being elucidated but these compounds might interact with other active compounds in flaxseed and contribute to biological activity attributed to other flax compounds. This review focuses on both the biological interaction of LOs with proteins and other molecules and comprehensive knowledge of LO pharmacological and biological properties. The physicochemical and nutraceutical properties of LOs, as well as the biological effects of certain LOs, and their underlying mechanisms of action, are reviewed. Finally, strategies for producing LOs by either peptide synthesis or recombinant organisms are presented. This review will be the first to describe LOs as a versatile scaffold for the action of compounds to deliver physiochemically/biologically active molecules for developing novel nutraceuticals and pharmaceuticals.

A review of flaxseed lignan and the extraction and refinement of secoisolariciresinol diglucoside.

Lignan is a class of diphenolic compounds that arise from the condensation of two phenylpropanoid moieties. Oilseed and cereal crops (e.g., flaxseed, sesame seed, wheat, barley, oats, rye, etc.) are major sources of plant lignan. Methods for commercial isolation of the lignan secoisolariciresinol diglucoside (SDG) are not well reported, as most publications describing the detection, extraction, and enrichment of SDG use methods that have not been optimized for commercial scale lignan recovery. Simply scaling up laboratory methods would require expensive infrastructure to achieve a marketable yield and reproducible product quality. Therefore, establishing standard protocols to produce SDG and its derivatives on an industrial scale is critical to decrease lignan cost and increase market opportunities. This review summarizes the human health benefits of flaxseed lignan consumption, lignan physicochemical properties, and mammalian lignan metabolism, and describes methods for detecting, extracting, and enriching flaxseed lignan. Refining and optimization of these methods could lead to the development of inexpensive lignan sources for application as an ingredient in medicines, dietary supplements, and other healthy ingredients.

Anti-Melanogenesis Effects of a Cyclic Peptide Derived from Flaxseed via Inhibition of CREB Pathway.

Linosorbs (Los) are cyclic peptides from flaxseed oil composed of the LO mixture (LOMIX). The activity of LO has been reported as being anti-cancer and anti-inflammatory. However, the study of skin protection has still not proceeded. In particular, there are poorly understood mechanisms of melanogenesis to LO. Therefore, we investigated the anti-melanogenesis effects of LOMIX and LO, and its activity was examined in mouse melanoma cell lines. The treatment of LOMIX (50 and 100 µg/mL) and LO (6.25-50 µM) suppressed melanin secretion and synthesis, which were 3-fold increased, in a dose-dependent manner, up to 95%. In particular, [1-9-NαC]-linusorb B3 (LO1) and [1-9-NαC]-linusorb B2 (LO2) treatment (12.5 and 25 µM) highly suppressed the synthesis of melanin in B16F10 cell lines up to 90%, without toxicity. LOMIX and LOs decreased the 2- or 3-fold increased mRNA levels, including the microphthalmia-associated transcription factor (MITF), Tyrosinase, tyrosinase-related protein 1 (TYRP1), and tyrosinase-related protein 2 (TYRP2) at the highest concentration (25 µM). Moreover, the treatment of 25 µM LO1 and LO2 inhibited the expression of MITF and phosphorylation of upper regulatory proteins such as CREB and PKA. Taken together, these results suggested that LOMIX and its individual LO could inhibit melanin synthesis via downregulating the CREB-dependent signaling pathways, and it could be used for novel therapeutic materials in hyperpigmentation.

Hypocholesterolemic Efficacy of Secoisolariciresinol Diglucoside and Its Polymer in Rat.

Hypercholesterolemia is a risk factor for cardiovascular disease. Conventional treatment methods include lifestyle changes and pharmaceutical interventions, but recently Health Canada approved a health claim for whole ground flaxseed as an alternative treatment for hypercholesterolemia. The literature suggests flaxseed lignans are responsible for the cholesterol-reducing effects of flaxseed. In this study, 96.1% secoisolariciresinol diglucoside (SDG) and a 50% SDG enriched polymer (SDG polymer) were investigated as treatments for hypercholesterolemia in rats. Wistar female rats were fed a 1% high-cholesterol diet for a one-week acclimatization prior to a 23-day intervention with enriched SDG or SDG polymer. A reduction in body weight normalized liver weight was observed in rats treated with enriched SDG when compared to the controls. Both enriched SDG (96.1%) and SDG polymer reduced serum triacylglycerol (19% and 15%, respectively) and increased high-density lipoprotein cholesterol (15% and 24%, respectively). Histopathologic analyses revealed lipid-lowering effects of either enriched SDG or SDG polymer along with lower steatosis scores and nonalcoholic fatty liver disease activity. Furthermore, the lack of statistical significance between SDG and SDG polymer treatment groups suggests that SDG polymer may be a potential alternative to enriched SDG for hypercholesterolemia with similar efficacy but lower cost.

Oral Pharmacokinetics of Enriched Secoisolariciresinol Diglucoside and Its Polymer in Rats.

Secoisolariciresinol diglucoside (SDG) is the principal lignan of flaxseed and precursor of its aglycone, secoisolariciresinol (SECO), and the mammalian lignans enterolactone (EL) and enterodiol (ED), the putative bioactive forms of oral administration of SDG. SDG is present in the seed hull as an ester-linked polymer. Although extraction and purification of SDG monomer is costly, the use of naturally occurring SDG in polymer form may offer a more economical approach for delivery of this precursor. The extent of SDG release from the polymer and subsequent bioavailability of SDG metabolites are unknown. To understand the relative bioavailability of SDG polymer, this study examined the comparative bioavailability of enriched SDG and SDG polymer in rats after a single oral SDG equivalent dose (40 mg/kg). A validated LC-MS/MS method quantified SDG and its metabolites in rat plasma following serial blood collections. SDG remained undetectable in rat plasma samples. Unconjugated SECO was detected in plasma after 0.25 h. Unconjugated ED was observed after 8 h (3.4 ± 3.3 ng/mL) and 12 h (6.2 ± 3.3 ng/mL) for enriched SDG and SDG polymer, respectively. Total (conjugated and unconjugated) ED and EL resulting from enriched SDG and SDG polymer reached similar maximal concentrations between 11 and 12 h and demonstrated similar total body exposures (AUC values). These data suggest a similar pharmacokinetic profile between the enriched and polymer form of SDG, providing support for the use of SDG polymer as a more economical precursor for SECO, ED, and EL in applications of chronic disease management.

The Anti-Cancer Effect of Linusorb B3 from Flaxseed Oil through the Promotion of Apoptosis, Inhibition of Actin Polymerization, and Suppression of Src Activity in Glioblastoma Cells.

Linusorbs (LOs) are natural peptides found in flaxseed oil that exert various biological activities. Of LOs, LOB3 ([1-9-NαC]-linusorb B3) was reported to have antioxidative and anti-inflammatory activities; however, its anti-cancer activity has been poorly understood. Therefore, this study investigated the anti-cancer effect of LOB3 and its underlying mechanism in glioblastoma cells. LOB3 induced apoptosis and suppressed the proliferation of C6 cells by inhibiting the expression of anti-apoptotic genes, B cell lymphoma 2 (Bcl-2) and p53, as well as promoting the activation of pro-apoptotic caspases, caspase-3 and -9. LOB3 also retarded the migration of C6 cells, which was achieved by suppressing the formation of the actin cytoskeleton critical for the progression, invasion, and metastasis of cancer. Moreover, LOB3 inhibited the activation of the proto-oncogene, Src, and the downstream effector, signal transducer and activator of transcription 3 (STAT3), in C6 cells. Taken together, these results suggest that LOB3 plays an anti-cancer role by inducing apoptosis and inhibiting the migration of C6 cells through the regulation of apoptosis-related molecules, actin polymerization, and proto-oncogenes.

Alginate Oligosaccharides: Production, Biological Activities, and Potential Applications.

Alginate, a group of polyuronic saccharides, has been widely used in both pharmaceutical and food industries due to its unique physicochemical properties as well as beneficial health effects. However, the potential applications of alginate are restricted because of its low water solubility and high solution viscosity when significant concentrations are needed, particularly in food products. Alginate oligosaccharides (AOS), oligomers containing 2 to 25 monomers, can be obtained via hydrolysis of glycosidic bonds, organic synthesis, or through biosynthesis. Generally, AOS have shorter chain lengths and thus improved water solubility when compared with higher molecular weight alginates of the same monomers. These oligosaccharides have attracted interest from both basic and applied researchers. AOS have unique bioactivity and can impart health benefits. They have shown immunomodulatory, antimicrobial, antioxidant, prebiotic, antihypertensive, antidiabetic, antitumor, anticoagulant, and other activities. As examples, they have been utilized as prebiotics, feed supplements for aquaculture, poultry, and swine, elicitors for plants and microorganisms, cryoprotectors for frozen foods, and postharvest treatments. This review comprehensively covers methods for AOS production from alginate, such as physical/chemical methods, enzymatic methods, fermentation, organic synthesis, and biosynthesis. Moreover, current progress in structural characterization, potential health benefits, and AOS metabolism after ingestion are summarized in this review. This review will discuss methods for producing and modified AOS with desirable structures that are suited for novel applications.

Novel flax orbitide derived from genetic deletion.

BACKGROUND: Flaxseed 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. RESULTS: Experimental 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). CONCLUSION: Comparison 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).

Vaccenic acid suppresses intestinal inflammation by increasing anandamide and related N-acylethanolamines in the JCR:LA-cp rat.

Vaccenic acid (VA), the predominant ruminant-derivedtransfat in the food chain, ameliorates hyperlipidemia, yet mechanisms remain elusive. We investigated whether VA could influence tissue endocannabinoids (ECs) by altering the availability of their biosynthetic precursor, arachidonic acid (AA), in membrane phospholipids (PLs). JCR:LA-cprats were assigned to a control diet with or without VA (1% w/w),cis-9,trans-11 conjugated linoleic acid (CLA) (1% w/w) or VA+CLA (1% + 0.5% w/w) for 8 weeks. VA reduced the EC, 2-arachidonoylglycerol (2-AG), in the liver and visceral adipose tissue (VAT) relative to control diet (P< 0.001), but did not change AA in tissue PLs. There was no additive effect of combining VA+CLA on 2-AG relative to VA alone (P> 0.05). Interestingly, VA increased jejunal concentrations of anandamide and those of the noncannabinoid signaling molecules, oleoylethanolamide and palmitoylethanolamide, relative to control diet (P< 0.05). This was consistent with a lower jejunal protein abundance (but not activity) of their degrading enzyme, fatty acid amide hydrolase, as well as the mRNA expression of TNFα and interleukin 1ß (P< 0.05). The ability of VA to reduce 2-AG in the liver and VAT provides a potential mechanistic explanation to alleviate ectopic lipid accumulation. The opposing regulation of ECs and other noncannabinoid lipid signaling molecules by VA suggests an activation of benefit via the EC system in the intestine.

Synthesis and Characterization of Site-Selective Orbitide-BSA Conjugate to Produce Antibodies.

Bioactive flax cyclic peptides (orbitides and linusorbs) were site-specifically ligated through methionine with bovine serum albumin (BSA) to produce immunogenic compounds. In this study, modified flaxseed immunosuppressant orbitides (linusorbs or LOs) containing hydroxyl (OH) groups were synthesized for use as haptens. These compounds were extensively characterized by 1H nuclear magnetic resonance (NMR), 13C NMR, high-performance liquid chromatography-tandem mass spectrometry, and Fourier transform infrared spectroscopy. The haptens were conjugated to BSA, and the extent of hapten incorporation was determined by matrix-assisted laser desorption and ionization, liquid chromatography-electrospray ionization-mass spectrometry, and sodium dodecyl sulfate polyacrylamide gel electrophoresis. The BSA hapten complexes were used to elicit polyclonal antibody (pAbs) production in rabbits. A competitive indirect enzyme-linked immunosorbent assay (CI-ELISA) was developed that used orbitide-specific pAbs and horseradish peroxidase (HRP) conjugates. The LO assay detection limit was approximately 0.01 µg/mL (ppm), and thus, ELISA can be used for the detection of LOs in tissue and plant samples. The pAbs can be used to detect and quantify LOs in flax and flaxseed samples, to verify the presence of LOs in flaxseed containing foods, and for the detection of LOs in tissue samples, wastes, and body fluids of animals fed flaxseed.

Nomenclature of homodetic cyclic peptides produced from ribosomal precursors: An IUPAC task group interim report.

In 2015, an International Union of Pure and Applied Chemistry (IUPAC) Task Group was formed to develop nomenclature recommendations for homodetic cyclic peptides produced from ribosomal precursors. Delegates of the 2015 International Conference on Circular Proteins (ICCP) were presented with the strengths and weaknesses of four published approaches to homodetic cyclic peptide nomenclature, and a summary of the ensuing discussion is presented here. This interim report presents a potentially novel suggestion-the use of Cahn-Ingold-Prelog rules to specify amino acid priority in homodetic peptides for consistent numbering. Indeed, this might be the first extension of the Cahn-Ingold-Prelog rules in five decades. The authors invite interested parties to contact the corresponding author with suggestions for the improvement of the proposed nomenclature; these ideas will be discussed and considered for inclusion in the final report.

Site Covalent Modification of Methionyl Peptides for the Production of FRET Complexes.

Flax cyclic peptides (orbitides, linusorbs (LOs)) [1-8-NαC],[1-MetO2]-linusorb B1 ([MetO2]-LO1) and [1-9-NαC],[1-MetO2]-linusorb B2 ([MetO2]-LO2) are biologically active. These LOs lack active nuclei commonly used in peptide modification. We have developed reactions to activate methionine methyl sulphide to produce stable derivatives. In these reactions, LOs are converted to sulfonium intermediates and subsequently to derivatives containing active nuclei while preserving their fundamental structures. The reaction conditions preserved cyclic peptide fundamental structure and organic solvent solubility. [Met]-LO1 and [Met]-LO2 analogues containing activated groups (-CN, -COOEt, and -NH2 ) in the form of methionine, methionine (S)-oxide, and methionine (S,S)-dioxide amino acids were synthesized and characterized by LCMS and 1D and 2D NMR spectroscopy. Coumarin orbitide complexes produced in this manner bind Eu(3+) yielding FRET compounds that absorb energy through coumarin antennae and emit photons at lanthanide wavelengths.

Proposed systematic nomenclature for orbitides.

Orbitides are short (5-11 amino acid residue), ribosomally synthesized homodetic plant cyclic peptides characterized by N-to-C amide bonds rather than disulfide bonds. Orbitides can be discovered using mass spectrometry of plant extracts or by identifying DNA sequences coding for the precursor protein. The number of orbitides that have been characterized to date, by a number of different research groups, is modest. The nomenclatural system currently used for the Type VI cyclic peptides has been developed in an ad hoc fashion and is somewhat arbitrary. We propose a systematic naming system specifically for the Type VI cyclic peptides that reflects the taxonomic name of the species producing the orbitides and a numbering system that enables systematic representation of amino acid residues and modifications. The proposed naming system emulates the IUPAC Nomenclature for Natural Products and UniProt, both of which use abbreviations of taxonomic names for the compounds in question. Nomenclature for post-translational modifications also follows the IUPAC precedent, as well as the cyclic peptide literature. Furthermore, the proposed system aims to maintain agreement with the precedents set by the pre-existing literature. An example of the proposed nomenclature is provided using the methionine-containing homodetic peptides of Linum usitatissimum (flaxseed).

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.