Sterol and phospholipid acyl chain alterations in Saccharomyces cerevisiae secretion mutants as a function of temperature stress

A conditional sterol esterification defect in yeast having either a sec1 or sec5 mutation in the secretory pathway

Two temperature-conditional secretory mutations, sec1 and sec5, cause the accumulation of post-Golgi vesicles when strains containing these mutations are grown at 37 degrees C. In addition to accumulating vesicles, the mutants do not esterify free sterol on rich media at the restrictive temperature. It is the high level of inositol in the media that causes this condition in the yeast Saccharomyces cerevisiae, not a defective steryl ester synthase or lack of substrates. When strains containing the sec1 or sec5 mutation were transformed separately with a plasmid carrying SEC1 and SEC5, the esterification and secretory defects were alleviated. Double mutants containing sec6, sec14 or sec18 with either a sec1 or sec5 mutation have normal esterification levels. Strains with suppressor mutations were isolated that grew at 37 degrees C, esterified sterols and had diminished accumulation of vesicles, when grown at the restrictive temperature on defined media with additional inositol. Electron microscopy was used to examine vesicle accumulation, the number of lipid droplets, and to further characterize the esterification defect. When grown at 37 degrees C on defined medium, the strains with sec5 or sec1 accumulated the usual secretory vesicles, but when grown under similar conditions with elevated levels of inositol, accumulated an additional vesicular-like body.

Microbial fatty acids and thermal adaptation

The existing literature on the role of fatty acids in microbial temperature adaptation is reviewed. Several modes of change of cellular fatty acids at varying environmental temperatures are shown to exist in yeasts and fungi, Gram-negative bacteria, and bacteria containing iso- and anteiso-branched fatty acids, as well as in a few Gram-positive bacteria. Consequently, the degree of fatty acid unsaturation and cyclization, fatty acid chain length, branching, and cellular fatty acid content increase, decrease, or remain unaltered on lowering the temperature. Moreover, microorganisms seem to be able to change from one mode or alter the cellular fatty acid profile temperature dependently to another on lowering the temperature, as well as even within the same growth temperature range, depending on growth conditions. Therefore, the effect of the temperature on cellular fatty acids appears to be more complicated than known earlier. However, similarities found in the modes of change of cellular fatty acids at varying environmental temperatures in several microorganisms within the above mentioned groups support the existence of a limited amount of common regulatory mechanisms. The models presented enable the prediction of temperature-induced changes occurring in the fatty acids of microorganisms, and enzymatic steps of the fatty acid biosynthesis that possibly are under temperature control.

High yield fermentation and purification of Tendamistat disulphide analogues secreted by Streptomyces lividans

In our studies of structure-function correlation of polypeptides we used Tendamistat (TM), an alpha-amylase-inhibitor of Streptomyces tendae, as a model to investigate the influence of different mutants on the expression and secretion of the protein. In addition, we examined the influence of replacing the two disulphide-bridges that stabilize the two-loop structure of the whole protein. The single mutants C27S, C27T, C45A, the double mutants C11A/C27A, C11A/C27S, C11A/C27T, C11A/C27L, C45/C73A and the fourfold mutant C11A/C27A/C45A/C73A were prepared. The mutated TM gene was expressed in S. lividans TK 24, which secretes the active form of the inhibitor into the culture medium. Compared with the wild-type, the double-mutated TM derivatives show an increase in secreted protein by a factor of two to ten. In contrast, the single-mutated inhibitor analogues show the reverse effect. In order to examine the influence of temperature and culture media on the production of protein derivative we used the most unstable C11A analogue. Our expression studies at 10, 19, 28 and 37 degrees C established 19 degrees C as the optimal temperature for production of the protein derivatives. The correlation between the stability and secretion of TM is discussed in the context of our knowledge of protein translocation in bacteria. Based on these experiments we optimized the fermentation parameters, isolated TM analogous on a large scale, and verified them.

Adaptational changes of fatty acid composition and the physical state of membrane lipids following the change of growth temperature in Yersinia enterocolitica

Yersinia enterocolitica is capable of growing in a broad range of temperatures from 4 to 45 C. How this organism alters its membrane lipids in response to the change of growth temperature is very interesting. The fatty acids of membrane lipids of cells cultured at 5, 15, 25 and 37 C were analyzed and the physical states of these membrane lipids were characterized. The major phospholipids of this bacterium were phosphatidylethanolamine, phosphatidylglycerol, cardiolipin, lysophosphatidylglycerol and lysophosphatidylethanolamine. No significant difference in phospholipid composition in response to culture temperatures was observed. It was reported in our previous paper that the major fatty acids of membrane phospholipids of Y. enterocolitica were C15:0, C16:0, C16:1, cyclopropane C17:0 and C18:0. Some differences in the fatty acid composition were, however, observed with the change of culture temperature. When the culture temperature was raised, the saturated and cyclopropane fatty acids substantially increased and the unsaturated ones decreased. A reverse phenomenon was observed when culture temperature was lowered. From the viewpoints of membrane physical state, adaptational changes were analyzed using a nylon microcapsule method. Phase transition in membrane lipids of cells grown at each culture temperature took place in the range of about 5 C below and about 10 C above the culture temperature. It is, therefore, considered that Y. enterocolitica maintains its membrane rigidity and fluidity in response to growth temperature by changing the membrane fatty acid composition.

Evidence for similarities and differences in the biosynthesis of fungal sterols

The sterol composition of two ascomycetous fungi, Saccharomyces cerevisiae and Gibberella fujikuroi, was examined by chromatographic (TLC, GLC, and HPLC) and spectral (MS and 1H-NMR) methods. Of notable importance was that both fungi produced cholesterol and a homologous series of long chain fatty alcohols (C22 to C30). In addition to ergosterol two novel sterols, ergosta-5,7, 9(11), 22-tetraenol and ergosterol endoperoxide, were isolated as minor compounds in growth-arrested cultures of yeast and in mycelia of G. fujikuroi. 24-Ethylidenelanosterol was also detected in mycelia of G. fujikuroi. A shift in sterol biosynthesis was observed by treatment with 24 (RS), 25-epiminolanosterol (an inhibitor of the S-adenosylmethionine C-24 transferase) and by monitoring the sterol composition at various stages of development. The results are interpreted to imply that the genes for 24-desalkyl, e.g., cholesterol, and 24-alkyl sterols, e.g., 24 beta- methyl cholesterol and 24-ethyl cholesterol, are distributed (but not always expressed) generally throughout the fungi but the occurrence of one or another compounds is influenced by the fitness (structure and amount) for specific sterols to act functionally during fungal ontogeny; sterol fitness is coordinated with Darwinian selection pressures.