Identification and characterization of a very long-chain fatty acid elongase gene in the methylotrophic yeast, Hansenula polymorpha

Overexpression of OLE1 Enhances Cytoplasmic Membrane Stability and Confers Resistance to Cadmium in Saccharomyces cerevisiae

The heavy metal cadmium is widely used and released into the environment, posing a severe threat to crops and humans. Saccharomyces cerevisiae is one of the most commonly used organisms in the investigation of environmental metal toxicity. We investigated cadmium stress and the adaptive mechanisms of yeast by screening a genome-wide essential gene overexpression library. A candidate gene, OLE1, encodes a delta-9 desaturase and was associated with high anti-cadmium-stress activity. The results demonstrated that the expression of OLE1 was positively correlated with cadmium stress tolerance and induction was independent of Mga2p and Spt23p (important regulatory factors for OLE1). Moreover, in response to cadmium stress, cellular levels of monounsaturated fatty acids were increased. The addition of exogenous unsaturated fatty acids simulated overexpression of OLE1, leading to cadmium resistance. Such regulation of OLE1 in the synthesis of unsaturated fatty acids may serve as a positive feedback mechanism to help cells counter the lipid peroxidation and cytoplasmic membrane damage caused by cadmium.

IMPORTANCE

A S. cerevisiae gene encoding a delta-9 desaturase, OLE1, was associated with high anti-cadmium-stress activity. The data suggest that the regulation of OLE1 in the synthesis of unsaturated fatty acids may serve as a positive feedback mechanism to help yeast cells counter the lipid peroxidation and cytoplasmic membrane damage caused by cadmium. The discovery of OLE1 involvement in membrane stability may indicate a novel defense strategy against cadmium stress.

Ketoacyl synthase domain is a major determinant for fatty acyl chain length in Saccharomyces cerevisiae

Yeast fatty acid synthase (Fas) comprises two subunits, α6 and β6, encoded by FAS2 and FAS1, respectively. To determine features of yeast Fas that control fatty acyl chain length, chimeric genes were constructed by combining FAS sequences from Saccharomyces cerevisiae (ScFAS) and Hansenula polymorpha (HpFAS), which mostly produces C16 and C18 fatty acids, respectively. The C16/C18 ratios decreased from 2.2 ± 0.1 in wild-type S. cerevisiae to 1.0 ± 0.1, 0.5 ± 0.2 and 0.8 ± 0.1 by replacement of ScFAS1, ScFAS2 and ScFAS1 ScFAS2 with HpFAS1, HpFAS2 and HpFAS1 HpFAS2, respectively, suggesting that the α, but not β subunits play a major role in determining fatty acyl chain length. Replacement of phosphopantetheinyl transferase (PPT) domain with the equivalent region from HpFAS2 did not affect C16/C18 ratio. Chimeric Fas2 containing half N-terminal ScFas2 and half C-terminal HpFas2 carrying H. polymorpha ketoacyl synthase (KS) and PPT gave a remarkable decrease in C16/C18 ratio (0.6 ± 0.1), indicating that KS plays a major role in determining chain length.

Comparative physiology of oleaginous species from the Yarrowia clade

Yarrowia lipolytica is a genetically tractable yeast species that has become an attractive model for analyses of lipid metabolism, due to its oleaginous nature. We investigated the regulation and evolution of lipid metabolism in non-Saccharomycetaceae yeasts, by carrying out a comparative physiological analysis of eight species recently assigned to the Yarrowia clade: Candida alimentaria, Y. deformans, C. galli, C. hispaniensis, C. hollandica, C. oslonensis, C. phangngensis and Y. yakushimensis. We compared the abilities of type strains of these species to grow on 31 non hydrophobic (sugars and other carbohydrate compounds) and 13 hydrophobic (triglycerides, alkanes and free fatty acids) carbon sources. Limited phenotypic diversity was observed in terms of the range of substrates used and, in the case of short-chain fatty acids, their toxicity. We assessed the oleaginous nature of these species, by evaluating their ability to store and to synthesize lipids. The mean lipid content of cells grown on oleic acid differed considerably between species, ranging from 30% of cell dry weight in C. oslonensis to 67% in C. hispaniensis. Lipid synthesis in cells grown on glucose resulted in the accumulation of C18:1 (n-9) as the major compound in most species, except for C. alimentaria and Y. yakushimensis, which accumulated principally C18:2(n-6), and C. hispaniensis, which accumulated both C16:0 and C18:1(n-9). Thus, all species of the clade were oleaginous, but they presented specific patterns of growth, lipid synthesis and storage, and therefore constitute good models for the comparative analysis of lipid metabolism in this basal yeast clade.

Cryptosporidium parvum long-chain fatty acid elongase

We report the presence of a new fatty acyl coenzyme A (acyl-CoA) elongation system in Cryptosporidium and the functional characterization of the key enzyme, a single long-chain fatty acid elongase (LCE), in this parasite. This enzyme contains conserved motifs and predicted transmembrane domains characteristic to the elongase family and is placed within the ELO6 family specific for saturated substrates. CpLCE1 gene transcripts are present at all life cycle stages, but the levels are highest in free sporozoites and in stages at 36 h and 60 h postinfection that typically contain free merozoites. Immunostaining revealed localization to the outer surface of sporozoites and to the parasitophorous vacuolar membrane. Recombinant CpLCE1 displayed allosteric kinetics towards malonyl-CoA and palmitoyl-CoA and Michaelis-Menten kinetics towards NADPH. Myristoyl-CoA (C14:0) and palmitoyl-CoA (C16:0) display the highest activity when used as substrates, and only one round of elongation occurs. CpLCE1 is fairly resistant to cerulenin, an inhibitor for both type I and II fatty acid synthases (i.e., maximum inhibitions of 20.5% and 32.7% were observed when C16:0 and C14:0 were used as substrates, respectively). These observations ultimately validate the function of CpLCE1.

Functional analysis of very long-chain fatty acid elongase gene, HpELO2, in the methylotrophic yeast Hansenula polymorpha

We describe the cloning and functional characterization of the fatty acid elongase gene HpELO2, a homologue of the HpELO1 gene required for the production of C24:0 in the yeast Hansenula polymorpha. The open reading frame (ORF) of HpELO2 consists of 1,035 bp, encoding 344 amino acids, sharing about 65% identity with that of Saccharomyces cerevisiae Elo2. Expression of HpELO2 rescued the lethality of the S. cerevisiae elo2Delta elo3Delta double disruptant. An accumulation of C18:0 and a significant increase and decrease in the levels of C24:0 and C26:0, respectively, were observed in the Hpelo2Delta disruptant. These results supported an idea that HpELO2 encodes a fatty acid elongase involved in the elongation of C18:0 to very long-chain fatty acids. The Hpelo1Delta Hpelo2Delta double disruption was nonviable, suggesting that HpELO1 and HpELO2 are the only two genes necessary for the biosynthesis in H. polymorpha. Interestingly, transcription of HpELO2 and HpELO1 were found to be transiently up-regulated by exogenous long-chain fatty acids; however, this up-regulation was not observed with HpELO1 and HpELO2 genes driven by the constitutively expressed promoter of the HpACT gene, suggesting that exogenous fatty acids specifically trigger the transcriptional induction of HpELO1 and HpELO2 through their promoter regions.