Identification of Antimicrobial Peptides of Native and Heated Hydrolysates from Hen Egg White Lysozyme

Characteristics of hen egg white lysozyme, strategies to break through antibacterial limitation, and its application in food preservation: A review

Hen egg white lysozyme (HEWL) is used as a food additive in China due to its outstanding antibacterial properties. It is listed as GRAS grade (generally recognized as safe) by the United States Food and Drug Administration (FDA, US) and has been extensively researched and used in food preservation. And the industrial production of HEWL already been realized. Given the complex food system that can affect the antibacterial activity of HEWL, and the limitations of HEWL itself on Gram-negative bacteria. Based on the structure and main biological characteristics of HEWL, this paper focuses on reviewing methods to enhance the stability and antibacterial properties of HEWL. Immobilization tactics such as chemically driven self-assembly, embedding and adsorption address the restriction of poor HEWL antibacterial activity effected by external factors. Both intermolecular and intramolecular modification strategies break the bactericidal deficiencies of HEWL itself. It also comprehensively analyzes the current application status and future prospects of HEWL in the food preservation. There was limited research on the biological methods in modifying HEWL. If the HEWL is genetically engineered, it can broaden its antimicrobial spectrum, improve its other biological activities, so as to further expand its application in the food industry. At present, research on HEWL mainly focused on its antibacterial properties, whereas its application in anti-inflammatory and antioxidant effects also presented great potential.

In vitro PCR verification that lysozyme inhibits nucleic acid replication and transcription

Lysozyme can kill bacteria by its enzymatic activity or through a mechanism involving its cationic nature, which can facilitate electrostatic interactions with the viral capsid, the negatively charged parts of nucleic acids, and polymerase, so binding to nucleic acids may be another biological function of lysozyme. Here, PCR was used as a research tool to detect the effects of lysozyme on the replication and transcription of nucleic acids after treatment in different ways. We found that lysozyme and its hydrolysate can enter cells and inhibit PCR to varying degrees in vitro, and degraded lysozyme inhibited nucleic acid replication more effectively than intact lysozyme. The inhibition of lysozyme may be related to polymerase binding, and the sensitivity of different polymerases to lysozyme is inconsistent. Our findings provide a theoretical basis for further explaining the pharmacological effects of lysozyme, such as antibacterial, antiviral, anticancer, and immune regulatory activities, and directions for the development of new pharmacological effects of lysozyme and its metabolites.

A Diphenylalanine Based Pentapeptide with Fibrillating Self-Assembling Properties

Peptides and their related compounds can self-assemble into diverse nanostructures of different shapes and sizes in response to various stimuli such as pH, temperature or ionic strength. Here we report the synthesis and characterization of a lysozyme derived pentapeptide and its ability to build well-defined fibrillar structures. Lysozyme FESNF peptide fragment was synthesized by solid phase peptide synthesis using the Fmoc/t-Bu strategy, purified by analytical high-performance liquid chromatography (HPLC) and its molecular weight was confirmed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Spectroscopic features of this pentapeptide were investigated by UV-visible spectroscopy and fluorimetry showing the pattern of marginal phenylalanine residues within the peptide sequence. Self-assembling properties were determined using atomic force microscopy (AFM), aggregation index and thioflavin T assay (ThT). FESNF generating fibrillar structures observed by AFM and aggregation propensity were primarily influenced by pH conditions. Moreover, the experimental data were confirmed by molecular dynamics simulation studies. The obtained fibrils will be used next to explore their potential to act as support material for medical and cosmetic application.

Centennial Review: The chicken yolk sac is a multifunctional organ

The yolk sac (YS) consists of the yolk, which supplies nutrients, and the YS tissue, which surrounds the yolk and provides essential metabolic functions for the developing embryo. The YS tissue is derived from the midgut of the embryo and consists of a layer of endodermal epithelial cells (EEC) in contact with the yolk contents, a mesodermal layer that contains the vascular system and an outer ectodermal layer. The YS tissue is a multifunctional organ that provides essential functions such as host immunity, nutrient uptake, carbohydrate and lipid metabolism, and erythropoiesis. The YS tissue plays a role in immunity by the transport of maternal antibodies in the yolk to the embryonic circulation that feeds the developing embryo. In addition, the YS tissue expresses high mRNA levels of the host defense peptide, avian β-defensin 10 during mid embryogenesis. Owing to its origin, the YS EEC share some functional properties with intestinal epithelial cells such as expression of transporters for amino acids, peptides, monosaccharides, fatty acids, and minerals. The YS tissue stores glycogen and expresses enzymes for glycogen synthesis and breakdown and glucogenesis. This carbohydrate metabolism may play an important role in the hatching process. The mesodermal layer of the YS tissue is the site for erythropoiesis and provides erythrocytes before the maturation of the bone marrow. Other functions of the YS tissue involve synthesis of plasma proteins, lipid transport and cholesterol metabolism, and synthesis of thyroxine. Thus, the YS is an essential organ for the growth, development, and health of the developing embryo. This review will provide an overview of the studies that have investigated the functionalities of the YS tissue at the cellular and molecular levels with a focus on chickens.

Transcriptome Analysis of Gene Expression in Dermacoccus abyssi HZAU 226 under Lysozyme Stress

Lysozyme acts as a kind of cationic antimicrobial protein and effectively hydrolyzes bacterial peptidoglycan to have a bactericidal effect, which also plays an important role in protecting eggs from microbial contamination. Dermacoccus abyssi HZAU 226, a Gram-positive bacterium isolated from spoiled eggs, has egg white and lysozyme tolerance, but its survival mechanism is unknown, especially from a transcriptomics point of view. In this study, the high lysozyme tolerance of D. abyssi HZAU 226 was characterized by three independent experiments, and then the Illumina RNA-seq was used to compare the transcriptional profiles of this strain in Luria–Bertani (LB) medium with and without 5 mg/mL lysozyme to identify differentially expressed genes (DEGs); 1024 DEGs were identified by expression analysis, including 544 up-regulated genes and 480 down-regulated genes in response to lysozyme treatment. The functional annotation analysis results of DEGs showed that these genes were mainly involved in glutathione biosynthesis and metabolism, ion transport, energy metabolism pathways, and peptidoglycan biosynthesis. This study is the first report of bacterial-related lysozyme RNA-seq, and our results help in understanding the lysozyme-tolerance mechanism of bacteria from a new perspective and provide transcriptome resources for subsequent research in related fields.

Production of White, Red and Black Quinoa (Chenopodium quinoa Willd Var. Real) Protein Isolates and Its Hydrolysates in Germinated and Non-Germinated Quinoa Samples and Antioxidant Activity Evaluation

Red, black and white seeds quinoa were germinated at 28 °C during 24 (G1), 48 and 72 h (G3). Red quinoa presented a higher percentage of germination with a value of 46% of germination at 72 h. Quinoa protein isolate (QPI) was obtained by alkaline extraction (pH 8.0) followed by an isoelectric precipitation (pH 4.5) from white, red and black quinoa seeds, germinated QPI-G1 or QPI-G3 and non-germinated QPI-NG, Chenopodium quinoa Willd var. Real. QPI-G1, QPI-G3 and QPI-NG were subject to a simulated gastric digestion (DG) and in vitro duodenal digestion (DD). The antioxidant activity was evaluated using the 1, 1-diphenyl-2-picryl hydrazyl (DPPH), azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and oxygen radical absorbance capacity (ORAC) methods. Gastric and duodenal digest of QPI-NG and QPI-G1 and QPI-G3 from white, red and black quinoa presented antioxidant activity. QPI-G1-DD of white quinoa presented the highest antioxidant activity with a DPPH value of 167.98 µmoL TE/g of digest, QPI-G1-DD of red quinoa with an ABTS value of 204.86 µmoL TE/g of digest and QPI-G1-DD of black quinoa with an ORAC value of 401.42 µmoL TE/g of digest. QPI-G3-DD of white quinoa presented higher antioxidant activity with a DPPH value of 186.28 µmoL TE/g of sample, QPI-G3-DD of red quinoa with an ABTS value of 144.06 µmoL TE/g of digest and QPI-G3-DD of black quinoa with an ORAC value of 395.14 µmoL TE/g of digest. The inhibition of reactive oxygen species (ROS) production in the zebrafish embryo model (Danio rerio) was evaluated. Protein profiles of QPI from white, red and black from germinated quinoa and non-germinated quinoa were similar with proteins between 10 kDa to 100 kDa with the presence of globulins 11S and 7S and 2S albumins.

Antibacterial Activity of Hen Egg White Lysozyme Denatured by Thermal and Chemical Treatments

The aim of this study was to increase the antibacterial spectrum of modified hen egg white lysozyme (HEWL) with thermal and chemical treatments against Gram-negative bacteria. The antibacterial activity of heat-denatured HEWL and chemical denatured HEWL against Gram-negative and Gram-positive bacteria was evaluated in 15 h of incubation tests. HEWL was denatured by heating at pH 6.0 and pH 7.0 and chemical denaturing was carried out for 1.0, 1.5, 2.0, and 4.0 h with DL-Dithiothreitol (DTT). HEWL modified by thermal and chemical treatments was characterized using the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) electrophoresis method. Heat-denatured HEWL lytic activity against Micrococcus lysodeikticus lessened with increasing temperature and time of incubation with the chemical agent (DTT). The loss of lytic activity in modified HEWL suggests that the mechanism of action of the antibacterial activity is not dependent on the lytic activity. Thermal and chemical treatments of HEWL enabled the production of oligoforms and increased antibacterial activity over a wider spectrum. Heat-denatured HEWL at pH 6.0 and chemically-denatured HEWL increased the HEWL antibacterial spectrum against Gram-negative bacteria (Escherichia coli ATCC 25922). HEWL at 120 °C and pH 6.0 (1.0 mg/mL) inhibited 78.20% of the growth of E. coli. HEWL/DTT treatment for 4.0 h (1.0 mg/mL) inhibited 68.75% of the growth E. coli. Heat-denatured HEWL at pH 6.0 and pH 7.0 and chemically-denatured HEWL (1.0, 1.5, 2.0, and 4.0 h with DTT) were active against Gram-positive bacteria (Staphylococcus carnosus CECT 4491T). Heat-denatured and chemical-denatured HEWL caused the death of the bacteria with the destruction of the cell wall. LIVE/DEAD assays of fluorescent dye stain of the membrane cell showed membrane perturbation of bacteria after incubation with modified HEWL. The cell wall destruction was viewed using electron microscopy. The results obtained in this study suggest that heat-denatured HEWL at pH 6.0 and chemical-denatured HEWL treatments increase the HEWL antibacterial activity against Gram-negative bacteria.