Advances in understanding of the oxysterol-binding protein homologous in yeast and filamentous fungi

Comparative proteomics reveals the mechanism of cyclosporine production and mycelial growth in Tolypocladium inflatum affected by different carbon sources

Cyclosporine A (CsA) is a secondary cyclopeptide metabolite produced by Tolypocladium inflatum that is widely used clinically as an immunosuppressant. CsA production and mycelial growth differed when T. inflatum was cultured in different carbon source media. During early fermentation, CsA was preferred to be produced in fructose medium, while the mycelium preferred to accumulate in sucrose medium. On the sixth day, the difference was most pronounced. In this study, high-throughput comparative proteomics methods were applied to analyze differences in protein expression of mycelial samples on day 6, revealing the proteins and mechanisms that positively regulate CsA production related to carbon metabolism. The differences included small molecule acid metabolism, lipid metabolism, organic catabolism, exocrine secretion, CsA substrate Bmt synthesis, and transcriptional regulation processes. The proteins involved in the regulation of mycelial growth related to carbon metabolism were also revealed and were associated with waste reoxidation processes or coenzyme metabolism, small molecule synthesis or metabolism, the stress response, genetic information or epigenetic changes, cell component assembly, cell wall integrity, membrane metabolism, vesicle transport, intramembrane localization, and the regulation of filamentous growth. This study provides a reliable reference for CsA production from high-efficiency fermentation. This study provides key information for obtaining more CsA high-yielding strains through metabolic engineering strategies.

Utilization of n-alkane and roles of lipid transfer proteins in Yarrowia lipolytica

Yarrowia lipolytica, a dimorphic yeast belonging to the Ascomycota, has potent abilities to utilize hydrophobic compounds, such as n-alkanes and fatty acids, as carbon and energy sources. Yarrowia lipolytica can synthesize and accumulate large amounts of lipids, making it a promising host to produce various lipids and convert n-alkanes to useful compounds. For advanced use of Y. lipolytica in these applications, it is necessary to understand the metabolism of these hydrophobic compounds in this yeast and the underlying molecular mechanisms. In this review, current knowledge on the n-alkane metabolism and how this is regulated in Y. lipolytica is summarized. Furthermore, recent studies revealed that lipid transfer proteins are involved in the utilization of n-alkanes and the regulation of cell morphology in response to n-alkanes. This review discusses the roles of membrane lipids in these processes in Y. lipolytica.

Aspergillus oryzae accelerates the conversion of ergosterol to ergosterol peroxide by efficiently utilizing cholesterol

It is well-known that excessive cholesterol leads to hypercholesterolemia, arteriosclerosis, coronary heart disease, stroke, and other diseases, which seriously threatens human health. Lactobacillus, a prokaryote, is reported to utilize cholesterol in the environment. However, little research focuses on the cholesterol utilization by eukaryote. Hence, the objectives of the present study were to investigate the mechanism of cholesterol utilization by the eukaryote and determine the role of oxysterol binding protein in this process. Our results showed for the first time that Aspergillus oryzae, a food-safe filamentous fungus, can utilize cholesterol efficiently. Our results also demonstrated that cholesterol utilization by A. oryzae might promote the conversion of ergosterol to ergosterol peroxide. Osh3, an oxysterol binding protein, can bind sterols (e.g., cholesterol, ergosterol, and ergosterol peroxide) and plays an important role in sterols transportation. This research is of considerable significance for developing low-fat food and cholesterol-lowering probiotics.