Conformational and ion-binding properties of cyclolinopeptide A isolated from linseed

Flaxseed Cyclic Peptide [1-9-NαC]-Linusorb B3 (CLA) Improves Oxidative Stability of Flaxseed Oil by Chelating Metal Ions and Intermediate Oxidative Products

Oxidative rancidity is a major issue limiting the utilization of flaxseed oil (FSO). Peptides possess an antioxidant effect; however, the flax cyclic peptide, a unique ingredient in FSO, has an obscure influence on the oxidation of FSO. Therefore, this study is aimed to investigate the effects of [1-9-NαC]-linusorb B3 (CLA) on the accelerated oxidation of FSO and the underlying mechanism. We found that CLA increased the antioxidant stability of refined flaxseed oil (RFO), indicated by the improved parameters involved in the oxidation after the addition of CLA. After accelerated oxidation, the acid value (AV) of the RFO was increased by 24.14 times, whereas that of the RFO with CLA (CLA-RFO) increased only by 7.21 times. Similarly, the peroxide value (POV) and P-anisidine value (P-AV) of CLA-RFO were significantly decreased. Besides, CLA influenced metal ions-induced oxidation. In the Cu2+ group, the addition of CLA reduced the AV by 18% and the POV by 20%. The results of the molecular docking analysis and fluorescence quenching showed that the metal ions and propionaldehyde interacted with the cavity of CLA, and propionaldehyde had the most stable binding configuration with CLA, indicating that CLA may slow down the oxidation of FSO by chelating the metal ions and the intermediate oxidative products.

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.

Birth of plant proteomics in India: a new horizon

In the post-genomic era, proteomics is acknowledged as the next frontier for biological research. Although India has a long and distinguished tradition in protein research, the initiation of proteomics studies was a new horizon. Protein research witnessed enormous progress in protein separation, high-resolution refinements, biochemical identification of the proteins, protein-protein interaction, and structure-function analysis. Plant proteomics research, in India, began its journey on investigation of the proteome profiling, complexity analysis, protein trafficking, and biochemical modeling. The research article by Bhushan et al. in 2006 marked the birth of the plant proteomics research in India. Since then plant proteomics studies expanded progressively and are now being carried out in various institutions spread across the country. The compilation presented here seeks to trace the history of development in the area during the past decade based on publications till date. In this review, we emphasize on outcomes of the field providing prospects on proteomic pathway analyses. Finally, we discuss the connotation of strategies and the potential that would provide the framework of plant proteome research.

BIOLOGICAL SIGNIFICANCE

The past decades have seen rapidly growing number of sequenced plant genomes and associated genomic resources. To keep pace with this increasing body of data, India is in the provisional phase of proteomics research to develop a comparative hub for plant proteomes and protein families, but it requires a strong impetus from intellectuals, entrepreneurs, and government agencies. Here, we aim to provide an overview of past, present and future of Indian plant proteomics, which would serve as an evaluation platform for those seeking to incorporate proteomics into their research programs. This article is part of a Special Issue entitled: Proteomics in India.

Effect of cyclolinopeptides on the oxidative stability of flaxseed oil

Polar compounds present in flaxseed oil increase its oxidative stability. Flaxseed oil becomes less stable to oxidation when filtered with silica. This observation may be linked to antioxidant compounds present in flaxseed oil. Flaxseed oil was passed over a silica adsorbent column to remove polar compounds. The polar compounds were then eluted from the silica absorbant using a series of increasingly polar solvents. The polar fractions from flaxseed oil were then added back to silica-treated flaxseed oil to determine the impact of fractions containing polar compounds on oxidative stability (induction time) at 100 °C. A polar fraction containing mainly cyclolinopeptide A (CLA, 1), but also containing β/γ- and δ-tocopherol increased the induction time of silica-treated flaxseed oil from 2.36 ± 0.28 to 3.20 ± 0.41 h. When oxidative stability was determined immediately after addition of the polar fractions other flaxseed fractions and solvent controls did not affect oil stability. However, when the oxidative stability index (OSI) test was delayed for three days and oil samples were held at room temperature after the addition of the polar fractions to the flaxseed oil, it was observed that the control oil treated with silica had become highly sensitive to oxidation. A polar fraction containing a mixture of CLs (1, 5, 7, 9, 11), improved the oxidative stability of peptide-free oil with respect to the control when the OSI measurement was made three days after adding the fraction. In addition, effects of 1 on the oxidative stability of peptide-free oil containing divalent metal cations was investigated.

Ion binding of cyclolinopeptide A: an NMR and CD conformational study

CD and nmr techniques have been used to study, in acetonitrile solution, the ion-complexing capability of cyclolinopeptide A (CLA), a cyclic nonapeptide of sequence cyclo-(Pro-Pro-Phe-Phe-Leu-Ile-Ile-Leu-Val) endowed with remarkable cytoprotective ability in vitro, and the conformation of the Ba(2+)/CLA complex. At room temperature, CLA in acetonitrile shows a proton nmr spectrum characteristic of the coexistence of many different conformers in intermediate exchange. The backbone contains a cis Pro-Pro bond, with all other peptide bonds in the trans conformation. CLA binds Ba2+ more tightly than the other cations studied, namely K+, Na+, Mg2+, and Ca2+; CD data are indicative of the presence of both 1:2 (sandwich) and 1:1 (equimolar) type complexes, depending on the Ba2+ ion concentration, whereas nmr data are consistent with an equimolar form. The relevant conformational features of the equimolar Ba2+/CLA complex are that the backbone contains all trans peptide bonds, a type I 6----3 beta-turn and a 3----1 gamma-turn (or a distorted 3----9 beta-turn). The global shape of the complexed peptide can be described as a bowl, with the concave (polar) side hosting Ba2+ and the convex side predominantly apolar.

Conformational analysis of cyclolinopeptide A, a cyclic nonapeptide: nuclear Overhauser effect and energy minimization studies

The conformation of cyclolinopeptide A [cyclo(Pro-Pro-Phe-Phe-Leu-Ile-Ile-Leu-Val)], a naturally occurring cyclic nonapeptide has been investigated in dimethylsulfoxide solution by 270 MHz 1H-nmr. A complete assignment of all C alpha H and NH resonances has been accomplished using two-dimensional correlated spectroscopy and nuclear Overhauser effects (NOEs). Analysis of interresidue NOEs and JHNC alpha H values permit construction of a molecular model for the cyclic peptide backbone. The crude model derived from nmr has been used as a starting point for energy minimization, which yields a refined structure largely compatible with nmr observations. The major features of the conformation of cyclolinopeptide A are a Type VI beta-turn centered at Pro(1)-Pro(2), with a cis peptide bond between these residues and a gamma-turn (C7 structure) centered at Ile(6). Two intramolecular hydrogen bonds Val(9) CO--Phe(3)NH (4----1) and Leu(5) CO--Ile(7)NH (3----1) are observed in the low-energy conformation. The limited solvent accessibility observed for the Val(9) and Leu(5) NH groups in the nmr studies are rationalized in terms of steric shielding.