Physicochemical properties, molecular structure, antioxidant activity, and biological function of extracellular melanin from Ascosphaera apis

Melanin in fungi: advances in structure, biosynthesis, regulation, and metabolic engineering

Fungi can synthesize a diverse range of melanins with appropriate physicochemical and biological characteristics for numerous applications in health, environmental protection, energy, and industry. Gaining deeper insights into the chemical structures, biosynthetic pathways, and regulatory mechanisms of fungal melanin would establish a basis for metabolic engineering approaches, aimed at enhancing production efficiency and creating custom-designed melanin with desirable material properties. Due to growing interest in their beneficial effects and applications, research on the structure, biosynthesis, and regulation of fungal melanin has significantly advanced. This review highlighted recent progress in fungal melanin production and applications, concentrating on structure, biosynthesis, and regulatory networks, and suggested how an improved understanding of melanin biosynthesis could enable efficient production for future applications.

Protective properties of melanin from lichen Lobaria pulmonaria (L.) HOFFM. In models of oxidative stress in skeletal muscle

Melanin is a dark pigment from the group of phenolic or indole polymers with inherent biocompatibility and antioxidant capacity. In extremophilic lichen Lobaria pulmonaria, melanin is responsible for protective properties against hostile environments. Herein, the ability of melanin extracted from L. pulmonaria to counteract oxidative stress and related damages was studied in the mouse diaphragm, the main respiratory muscle. Initial in vitro experiments demonstrated ultraviolet (UV)-absorbing, antioxidant and metal chelating activities of melanin. This melanin can form nanoparticles and stabile colloidal system at concentration of 5 μg/ml. Pretreatment of the muscle with melanin (5 μg/ml) markedly reduced UV-induced increase in intracellular and extracellular reactive oxygen species (ROS) as well as antimycin A-mediated enhancement in mitochondrial ROS production accompanied by lipid peroxidation and membrane asymmetry loss. In addition, melanin attenuated suppression of neuromuscular transmission and alterations of contractile responses provoked by hydrogen peroxide. Thus, this study shed the light on the perspectives of the application of a lichen melanin as a protective component for treatment of skeletal muscle disorders, which are accompanied with an increased ROS production.

Optimized Separation of Carthamin from Safflower by Macroporous Adsorption Resins and Its Protective Effects on PC12 Cells Injured by OGD/R via Nrf2 Signaling Pathway

The growing demand for safe natural products has reignited people's interest in natural food pigments. Here, we proposed the use of macroporous adsorption resins (MARs) to separate and purify carthamin from safflower. The optimal parameters for carthamin purification with HPD400 MAR were determined as follows: a mass ratio of crude carthamin in sample solution to wet resin of 0.3, a crude carthamin solution concentration of 0.125 g·mL-1, a pH of 6.00, a sample volume flow rate of 0.5 mL·min-1, an ethanol volume fraction of 58%, an elution volume of 4 BV, and an elution volume flow rate of 1.0 mL·min-1. Under the above purification conditions, the recovery rate of carthamin was above 96%. Carthamin dramatically improved the survival rate of PC12 cells damaged by oxygen-glucose deprivation/reoxygenation and protected them from oxidative stress by inhibiting the generation of reactive oxygen species and increasing the total antioxidant capacity and glutathione (GSH) levels. Carthamin promoted extracellularly regulated protein kinase phosphorylation into the nucleus, permitting Nrf2 nuclear translocation and upregulating the gene expression of the rate-limiting enzymes glutamate-cysteine ligase catalytic subunit and glutamate-cysteine ligase regulatory subunit of GSH synthesis to obliterate free radicals and exert antioxidant effects. This study revealed the purification method of carthamin and its antioxidant protective effects, providing important insights into the application of carthamin in functional foods.

StcU-2 Gene Mutation via CRISPR/Cas9 Leads to Misregulation of Spore-Cyst Formation in Ascosphaera apis

Ascosphaera apis is the causative agent of honey bee chalkbrood disease, and spores are the only known source of infections. Interference with sporulation is therefore a promising way to manage A. apis. The versicolorin reductase gene (StcU-2) is a ketoreductase protein related to sporulation and melanin biosynthesis. To study the StcU-2 gene in ascospore production of A. apis, CRISPR/Cas9 was used, and eight hygromycin B antibiotic-resistant transformants incorporating enhanced green fluorescent protein (EGFP) were made and analyzed. PCR amplification, gel electrophoresis, and sequence analysis were used for target gene editing analysis and verification. The CRISPR/Cas9 editing successfully knocked out the StcU-2 gene in A. apis. StcU-2 mutants had shown albino and non-functional spore-cyst development and lost effective sporulation. In conclusion, editing of StcU-2 gene has shown direct relation with sporulation and melanin biosynthesis of A. apis; this effective sporulation reduction would reduce the spread and pathogenicity of A. apis to managed honey bee. To the best of our knowledge, this is the first time CRISPR/Cas9-mediated gene editing has been efficiently performed in A. apis, a fungal honey bee brood pathogen, which offers a comprehensive set of procedural references that contributes to A. apis gene function studies and consequent control of chalkbrood disease.