Alteration In Sterol Composition Research Articles

Deletion of the Candida albicans TLO gene family results in alterations in membrane sterol composition and fluconazole tolerance.

Development of resistance and tolerance to antifungal drugs in Candida albicans can compromise treatment of infections caused by this pathogenic yeast species. The uniquely expanded C. albicans TLO gene family is comprised of 14 paralogous genes which encode Med2, a subunit of the multiprotein Mediator complex which is involved in the global control of transcription. This study investigates the acquisition of fluconazole tolerance in a mutant in which the entire TLO gene family has been deleted. This phenotype was reversed to varying degrees upon reintroduction of representative members of the alpha- and beta-TLO clades (i.e. TLO1 and TLO2), but not by TLO11, a gamma-clade representative. Comparative RNA sequencing analysis revealed changes in the expression of genes involved in a range of cellular functions, including ergosterol biosynthesis, mitochondrial function, and redox homeostasis. This was supported by the results of mass spectrometry analysis, which revealed alterations in sterol composition of the mutant cell membrane. Our data suggest that members of the C. albicans TLO gene family are involved in the control of ergosterol biosynthesis and mitochondrial function and may play a role in the responses of C. albicans to azole antifungal agents.

Phenotypic Analysis of Mutants of Ergosterol Biosynthesis Genes (ERG3 and ERG4) in the Red Yeast Xanthophyllomyces dendrorhous.

Xanthophyllomyces dendrorhous synthesizes astaxanthin, a carotenoid used in aquaculture. Astaxanthin is synthesized from metabolites of the mevalonate pathway, which are also precursors for sterols biosynthesis. The interruption of the CYP61 gene, which is involved in the synthesis of ergosterol (mutant CBS.cyp61–), resulted in a phenotype that overproduces carotenoids due to the activation of the SREBP pathway. In this work, we constructed other mutants of ergosterol biosynthesis in this yeast to evaluate whether they have the same phenotype as mutant CBS.cyp61–. By bioinformatic analysis, the ERG3 and ERG4 genes of X. dendrorhous were identified, and each gene was deleted in the wild-type strain. Mutants CBS.Δerg3 and CBS.Δerg4 did not produce ergosterol; CBS.Δerg3 primarily accumulated episterol, and CBS.Δerg4 primarily accumulated ergosta-5,7,22,24(28)-tetraenol. The transcription levels of the HMGS gene of the mevalonate pathway were evaluated by RT-qPCR, which showed a slight increase in CBS.Δerg4, but the transcription levels were still 10-fold lower than in strain CBS.cyp61–. Both CBS.Δerg3 and CBS.Δerg4 did not overproduce carotenoids, even though they do not produce ergosterol. Thus, the results of this study indicate that the absence of ergosterol does not activate the SREBP pathway in X. dendrorhous, but rather it depends on other alterations in sterol composition.

Eudesmane sesquiterpenes from Chinese liverwort are substrates of Cdrs and display antifungal activity by targeting Erg6 and Erg11 of Candida albicans

We isolated twelve sesquiterpenes from Chinese liverwort Tritomaria quinquedentata (Huds.) Buch., including four new compounds. Among them, five eudesmane sesquiterpenes were ineffective against Candida albicans wild strain SC5314 but active towards efflux pumps-deficient strain DSY654 using Alamar blue assay. Further test of the most active agent of ent-isoalantolactone (8, ent-iLL) showed that it also inhibited the yeast-to-hyphal switch of DSY654 cells. The intracellular content measurement using high performance liquid chromatography (HPLC) revealed that ent-iLL was intracellularly accumulated in C. albicans when efflux pumps were deficient or inhibited by Cdrs inhibitor riccardin D, suggesting that the activity of ent-iLL was compromised by efflux pumps Cdrs. Moreover, ent-iLL potentially inhibited the activity of Erg11 and Erg6 of DSY654 and thereby resulted in the alteration of sterol composition by decreasing ergosterol contents and increasing zymosterol and lanosterol accumulation. Our study demonstrated that eudesmane sesquiterpenes, as the substrates of Cdrs, could interfere with sterol synthesis of C. albicans to exert antifungal activity when co-applied with Cdrs inhibitors.

Plasma membrane lipid–protein interactions affect signaling processes in sterol-biosynthesis mutants in Arabidopsis thaliana

The plasma membrane is an important organelle providing structure, signaling and transport as major biological functions. Being composed of lipids and proteins with different physicochemical properties, the biological functions of membranes depend on specific protein–protein and protein–lipid interactions. Interactions of proteins with their specific sterol and lipid environment were shown to be important factors for protein recruitment into sub-compartmental structures of the plasma membrane. System-wide implications of altered endogenous sterol levels for membrane functions in living cells were not studied in higher plant cells. In particular, little is known how alterations in membrane sterol composition affect protein and lipid organization and interaction within membranes. Here, we conducted a comparative analysis of the plasma membrane protein and lipid composition in Arabidopsis sterol-biosynthesis mutants smt1 and ugt80A2;B1. smt1 shows general alterations in sterol composition while ugt80A2;B1 is significantly impaired in sterol glycosylation. By systematically analyzing different cellular fractions and combining proteomic with lipidomic data we were able to reveal contrasting alterations in lipid–protein interactions in both mutants, with resulting differential changes in plasma membrane signaling status.

Effects of antimycotic azoles on growth and sterol biosynthesis of Leishmania promastigotes

Promastigotes of 36 World Health Organization reference (and other) strains of 6 species and 10 subspecies of Leishmania were cultured in the presence of 3 antimycotic azole drugs (ketoconazole, itraconazole, fluconazole) and their population growth determined. A representative of each subspecies was also analyzed for its sterol composition. For all strains the order of azole drug activity with respect to both growth and sterol biosynthesis inhibition was itraconazole ≧ ketoconazole > fluconazole . The inhibitory actions of the three azole drugs were greater on L. donovani and L. braziliensis subspecies and on L. mexicana amazonensis than on L. aethiopica, L. major, L. tropica and L. mexicana mexicana. The nature of the changes in sterol composition caused by the drugs was the same for all strains. The normal, major endogenous sterols of the promastigotes (5-dehydroepisterol and ergosterol) were reduced in amount to 1–2% of the total free sterols and were replaced by endogenous 14α-methyl sterols and exogenous cholesterol. The changes occurred rapidly, were drug concentration dependent and coincided with growth inhibition. Six strains of those Leishmania species less sensitive to the azole drugs could be subcultured indefinitely at reduced growth rates in the presence of a ketoconazole concentration causing the same extraordinary alterations in sterol composition. This suggested that the bulk membrane functions of sterols in leishmanias can be served by 14α-methyl sterols and cholesterol, albeit imperfectly, while traces of 14α-desmethyl sterols are needed for uncharacterized metabolic functions.

Effect of Alteration of Sterol Composition on the Salt Sensitivity of a Tobacco Cell Suspension Culture

Effect of Alteration of Sterol Composition on the Salt Sensitivity of a Tobacco Cell Suspension Culture

The effects of azole and polyene antifungals on the plasma membrane enzymes of Candida albicans.

The two clinically important classes of antimycotic drugs, the polyenes and azoles, act on the plasma membrane of the cell. The primary modes of action are believed to be through interaction with sterols (polyenes) and alteration in sterol composition of the membrane (azoles). In this report we show that, at growth inhibitory concentrations, the polyenes (nystatin and amphotericin) and azoles (miconazole and ketoconazole) also inhibit plasma membrane enzymes. There was extensive (greater than 75%) inhibition of the Candida albicans plasma membrane enzymes ATPase, glucan synthase, adenyl cyclase and 5'-nucleotidase, when assayed in situ. The antifungals papulacandin and echinocandin, which inhibit glucan synthesis, also inhibited plasma membrane enzymes in situ; glucan synthase (greater than 90%), 5'-nucleotidase (greater than 80%) and ATPase (70-80%). Purified plasma membrane was prepared from yeast cells of C. albicans by two different techniques: concanavalin A stabilization and coating of spheroplasts with silica microbeads. In the purified plasma membrane vesicles prepared from concanavalin A the adenyl cyclase and phosphodiesterase were extensively (greater than 90%) inhibited by the three different classes of antifungal drugs; variable inhibition was observed with ATPase (70-100%). The 3',5'-cyclic phosphodiesterase of the plasma membrane purified by the microbeads method was almost completely inhibited by all of the antifungals tested and there was partial inhibition of ATPase (20-85%) and adenyl cyclase (30-90%).

Increased drug sensitivity inCandida albicanscells accumulating 14-methylated sterols

Multiple increases in drug sensitivity were observed in Candida albicans cells that were accumulating 14-methylated sterols as a result of a mutation or clotrimazole treatment. The possibility was suggested that a change in membrane permeability caused by the alteration in sterol composition was responsible for the increased susceptibility.

Accumulation of 14-methyl sterols and defective hyphal growth in Candida albicans.

Polyene-resistant mutants of Candida albicans accumulating 14-methyl sterols in place of ergosterol and defective in hyphal growth were isolated after ultraviolet mutagenesis. Analysis of revertants showed that the alteration in sterol composition, the inability to grow as hyphae, and the antibiotic resistance had returned to normal simultaneously. In addition, clotrimazole, which caused accumulation of 14-methyl sterols at a subfungistatic concentration, also inhibited hyphal formation but had little effect on yeast propagation. It is concluded that there is an intrinsic rather than a fortuitous relationship between sterol composition and morphogenesis.

Filipin/sterol complexes in fertilized and unfertilized sea urchin egg membranes.

Sea urchin (Arbacia punctulata) eggs and zygotes were treated with filipin in an effort to examine changes in membrane sterols at fertilization. The plasma membrane of treated unfertilized eggs possessed numerous filipin/sterol complexes, while fewer complexes were associated with membranes delimiting cortical granules, demonstrating that the plasmalemma is relatively rich in beta-hydroxysterols in comparison to cortical granule membrane. Following fusion with the plasmalemma, membrane formerly delimiting cortical granules underwent a dramatic alteration in sterol composition, as indicated by a rapid increase in the number of filipin/sterol complexes. In contrast, portions of the zygote plasma membrane, derived from the plasmalemma of the unfertilized egg, displayed little or no change in filipin/sterol composition. Other than regions of the plasma membrane engaged in endocytosis, the plasmalemma of the zygote possessed a homogeneous distribution of filipin/sterol complexes and appeared similar to that of the unfertilized egg. These results demonstrate that following its fusion with the egg plasmalemma, membranes, formerly delimiting cortical granules, undergo a dramatic alteration in sterol composition. Changes in the localization of filipin/sterol complexes are discussed in reference to alterations in egg plasmalemmal function at fertilization.

Thiamine-induced alteration in sterol composition of Saccharomyces carlsbergensis 4228

The cells of Saccharomyces carlsbergensis 4228 grown with added thiamine in a vitamin B-6-free medium did not contain ergosterol and zymosterol (the predominant sterols in cells grown without thiamine). Instead, significant amounts of squalene, lanosterol and unidentified sterols accumulated in the thiamine-grown cells. Of the unidentified sterols, the most predominant was Δ 5,7-ergostadien-3β-ol at 26.0% of the total sterol. The accumulation of this sterol in the place of ergosterol (Δ 5,7,22-ergostatrien-3β-ol) indicates that the desaturation at C-22 of sterol structure is completely blocked in the thiamine-grown cells. On the basis of chromatographic behaviours, the structures of other unidentified sterols were assumed to be 4α-methyl-Δ 8,24(25)-cholestadien-3β-ol, 4α-methyl-Δ 8,24(28)-ergostadien-3β-ol, Δ 8,24(28)-ergostadien-3β-ol and Δ 5,7,24(28)_ergostatrien-3β-ol. The accumulation of 4α-methyl sterols, in addition to that of a large amount of lanosterol (48.4% of total sterol), suggests that the demethylation processes from lanosterol to zymosterol was partially depressed in the thiamine-grown cells.