Evaluation of sterol transport from the endoplasmic reticulum to mitochondria using mitochondrially targeted bacterial sterol acyltransferase in Saccharomyces cerevisiae

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.

Mitochondrial Effects in the Liver of C57BL/6 Mice by Low Dose, High Energy, High Charge Irradiation

Galactic cosmic rays are primarily composed of protons (85%), helium (14%), and high charge/high energy ions (HZEs) such as ⁵⁶Fe, ²⁸Si, and ¹⁶O. HZE exposure is a major risk factor for astronauts during deep-space travel due to the possibility of HZE-induced cancer. A systems biology integrated omics approach encompassing transcriptomics, proteomics, lipidomics, and functional biochemical assays was used to identify microenvironmental changes induced by HZE exposure. C57BL/6 mice were placed into six treatment groups and received the following irradiation treatments: 600 MeV/n ⁵⁶Fe (0.2 Gy), 1 GeV/n ¹⁶O (0.2 Gy), 350 MeV/n ²⁸Si (0.2 Gy), ¹³⁷Cs (1.0 Gy) gamma rays, ¹³⁷Cs (3.0 Gy) gamma rays, and sham irradiation. Left liver lobes were collected at 30, 60, 120, 270, and 360 days post-irradiation. Analysis of transcriptomic and proteomic data utilizing ingenuity pathway analysis identified multiple pathways involved in mitochondrial function that were altered after HZE irradiation. Lipids also exhibited changes that were linked to mitochondrial function. Molecular assays for mitochondrial Complex I activity showed significant decreases in activity after HZE exposure. HZE-induced mitochondrial dysfunction suggests an increased risk for deep space travel. Microenvironmental and pathway analysis as performed in this research identified possible targets for countermeasures to mitigate risk.

In-vitro GIT Tolerance of Microencapsulated Bifidobacterium bifidum ATCC 35914 Using Polysaccharide-Protein Matrix

Longevity of probiotic is the main concern for getting maximum benefits when added in food product. Bifidobacterium, a probiotic, tends to lose its viability during gastrointestinal track (GIT) transit and storage of food. Their viability can be enhanced through microencapsulation technology. In this study, Bifidobacterium bifidum (B. bifidum) ATCC 35914 was encapsulated by using two experimental plans. In the first plan, chitosan (CH) at 0.6, 0.8, and 1.0% and sodium alginate (SA) at 4, 5, and 6% were used. Based on encapsulation efficiency, 6% sodium alginate and 0.8% chitosan were selected for single coating of the bacteria, and the resulting micro beads were double coated with different concentrations (5, 7.5, and 10%) of whey protein concentrate (WPC) in the second plan. Encapsulation efficiency and GIT tolerance were determined by incubating the micro beads in simulated gastrointestinal juices (SIJ) at variable pH and exposure times, and their release (liberation of bacterial cells) profile was also observed in SIJ. The microencapsulated bacterial cells showed significantly (P < 0.01) higher viability as compared to the unencapsulated (free) cells during GIT assay. The double-coated micro beads SA 6%-WPC 5% and CH 0.8%-WPC 5% were proven to have the higher survival at pH 3.0 after 90 min of incubation time and at pH 7.0 after 3-h exposure in comparison to free cells in simulated conditions of the stomach and intestine, respectively. Moreover, double coating with whey protein concentrate played a significant role in the targeted (10^6-9 CFU/mL) delivery under simulated intestinal conditions.

The yeast pantothenate kinase Cab1 is a master regulator of sterol metabolism and of susceptibility to ergosterol biosynthesis inhibitors

In fungi, ergosterol is an essential component of the plasma membrane. Its biosynthesis from acetyl-CoA is the primary target of the most commonly used antifungal drugs. Here, we show that the pantothenate kinase Cab1p, which catalyzes the first step in the metabolism of pantothenic acid for CoA biosynthesis in budding yeast (Saccharomyces cerevisiae), significantly regulates the levels of sterol intermediates and the activities of ergosterol biosynthesis-targeting antifungals. Using genetic and pharmacological analyses, we show that altered pantothenate utilization dramatically alters the susceptibility of yeast cells to ergosterol biosynthesis inhibitors. Genome-wide transcription and MS-based analyses revealed that this regulation is mediated by changes both in the expression of ergosterol biosynthesis genes and in the levels of sterol intermediates. Consistent with these findings, drug interaction experiments indicated that inhibition of pantothenic acid utilization synergizes with the activity of the ergosterol molecule-targeting antifungal amphotericin B and antagonizes that of the ergosterol pathway-targeting antifungal drug terbinafine. Our finding that CoA metabolism controls ergosterol biosynthesis and susceptibility to antifungals could set the stage for the development of new strategies to manage fungal infections and to modulate the potency of current drugs against drug-sensitive and -resistant fungal pathogens.

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

Oxysterol-binding protein is an important non-vesicular trafficking protein involved in the transportation of lipids in eukaryotic cells. Oxysterol-binding protein is identified as oxysterol-binding protein-related proteins (ORPs) in mammals and oxysterol-binding protein homologue (Osh) in yeast. Research has described the function and structure of oxysterol-binding protein in mammals and yeast, but little information about the protein's structure and function in filamentous fungi has been reported. This article focuses on recent advances in the research of Osh proteins in yeast and filamentous fungi, such as Aspergillus oryzae, Aspergillus nidulans, and Candida albicans. Furthermore, we point out some problems in the field, summarizing the membrane contact sites (MCS) of Osh proteins in yeast, and consider the future of Osh protein development.

Oxysterol-binding protein homologs mediate sterol transport from the endoplasmic reticulum to mitochondria in yeast

Sterols are present in eukaryotic membranes and significantly affect membrane fluidity, permeability, and microdomain formation. They are synthesized in the endoplasmic reticulum (ER) and transported to other organelles and the plasma membrane. Sterols play important roles in the biogenesis and maintenance of mitochondrial membranes. However, the mechanisms underlying ER-to-mitochondrion sterol transport remain to be identified. Here, using purified yeast membrane fractions enriched in ER and mitochondria, we show that the oxysterol-binding protein homologs encoded by the OSH genes in the yeast Saccharomyces cerevisiae mediate sterol transport from the ER to mitochondria. Combined depletion of all seven Osh proteins impaired sterol transport from the ER to mitochondria in vitro; however, sterol transport was recovered at different levels upon adding one of the Osh proteins. Of note, the sterol content in the mitochondrial fraction was significantly decreased in vivo after Osh4 inactivation in a genetic background in which all the other OSH genes were deleted. We also found that Osh5-Osh7 bind cholesterol in vitro We propose a model in which Osh proteins share a common function to transport sterols between membranes, with varying contributions by these proteins, depending on the target membranes. In summary, we have developed an in vitro system to examine intracellular sterol transport and provide evidence for involvement of Osh proteins in sterol transport from the ER to mitochondria in yeast.