Active Peptide AR-9 From Eupolyphaga sinensis Reduces Blood Lipid and Hepatic Lipid Accumulation by Restoring Gut Flora and Its Metabolites in a High Fat Diet–Induced Hyperlipidemia Rat

The dysbiosis of gut flora and its metabolites plays important roles in the progression of hyperlipidemia (HL), and some bioactive peptides are available for HL treatment. In this study, we aimed to isolate an active peptide (AR-9) from active peptides of E. sinensis (APE) and determine whether AR-9 could improve many symptoms of a HL rat induced by a high-fat diet (HFD) by modulating gut flora and its metabolites. Above all, AR-9 was derived from APE using ion-exchange chromatography, and its structure was deconstructed by Fourier transform infrared spectrometer (FT-IR), circular dichroism (CD) spectroscopy, and UHPLC-Q-Exactive-Orbitrap MS. Then, an HFD-induced HL model in SD rats was established and used to clarify the regulatory effects of AR-9 (dose of 3 mg/kg) on HL. Normal diet–fed rats were taken as the control. The plasma samples and liver were harvested for biochemical and histopathological examinations. 16S rRNA gene sequencing and untargeted metabolomics were sequenced to assess changes in gut flora and its metabolites from rat fecal samples. Finally, Spearman’s correlation analysis was used to assess the relationship between lipid-related factors, gut flora, and its metabolites so as to evaluate the mechanism of AR-9 against HL. The results of the separation experiments showed that the amino acid sequence of AR-9 was AVFPSIVGR, which was a fragment of the actin protein from Blattaria insects. Moreover, HFD rats developed exaltation of index factors, liver lipid accumulation, and simple fibrosis for 8 weeks, and the profiles of gut flora and its metabolites were significantly altered. After treatment, AR-9 decreased the levels of lipid factors in plasma and the extent of liver damage. 16S rRNA gene sequencing results indicated that AR-9 significantly increased the relative abundance of beneficial bacteria Bacteroidetes and reduced the relative abundance of the obesity-associated bacteria Firmicutes. Furthermore, AR-9 changed gut microbiota composition and increased the relative abundance of beneficial bacteria: Lactobacillus, Clostridium, Dehalobacterium, and Candidatus arthromitus. Fecal metabolomics showed that the pathway regulated by AR-9 was “arginine biosynthesis”, in which the contents were citrulline and ornithine. Spearman’s correlation analysis revealed that two metabolites (ornithine and citrulline) showed significantly negative correlations with obesity-related parameters and positive correlations with the gut genera (Clostridium) enriched by AR-9. Overall, our results suggested interactions between gut microbial shifts and fecal amino acid/lipid metabolism and revealed the mechanisms underlying the anti-HL effect of AR-9. The abovementioned results not only reveal the initial anti-HL mechanism of AR-9 but also provide a theoretical basis for the continued development of AR-9.

Experimental Assignment of Disulfide-Bonds in Purified Proteins

The formation of disulfide bonds in proteins is an important post-translational modification that is critical for stabilizing the native structures of proteins, particularly proteins exposed to oxidizing environments. For this reason, most cysteines in secreted proteins or protein domains on the surface of the cell are in disulfides, whereas most cysteines in the cytoplasm are in the unmodified -SH form. Disulfide linkages must be experimentally determined, as they cannot be predicted from amino acid sequence. These assignments provide insights into three-dimensional structure and contribute to the understanding of structural-functional relationships. This unit details a series of protocols that have been applied successfully to map disulfide bonds in proteins. The general strategy involves chemical or proteolytic cleavage of the protein followed by chromatographic separation of the resultant peptides. Mass spectrometry is used to identify disulfide-containing peptides and determine sites of disulfide linkage. A partial reduction and alkylation strategy for mapping disulfide linkages in peptides with multiple disulfide bonds is also presented. © 2019 by John Wiley & Sons, Inc.

Modification of Cysteine

This unit describes a number of methods for modifying cysteine residues of proteins and peptides. A general procedure for alkylation of cysteine residues in a protein of known size and composition with haloacyl reagents or N-ethylmaleimide (NEM) is presented, and alternate protocols describe similar procedures for use when the size and composition are not known and when only very small amounts of protein are available. Alkylations that introduce amino groups using bromopropylamine and N-(iodoethyl)-trifluoroacetamide are also presented. Two procedures that are often used for subsequent sequence analysis of the protein, alkylation with 4-vinylpyridine and acrylamide, are described, and a specialized procedure for 4-vinylpyridine alkylation of protein that has been adsorbed onto a sequencing membrane is also presented. Reversible modification of cysteine residues by way of sulfitolysis is described, and a protocol for oxidation with performic acid for amino acid compositional analysis is also provided. Gentle oxidation of cysteine residues to disulfides by exposure to air is described. Support protocols are included for recrystallization of iodoacetic acid, colorimetric detection of free sulfhydryls, and desalting of modified samples. © 2017 by John Wiley & Sons, Inc.