Rodríguez-Vargas Sonia, Sánchez-García Alicia, Martínez-Rivas Jose Manuel, Prieto Jose Antonio, Randez-Gil Francisca
Department of Biotechnology, Instituto de Agroquímica y Tecnología de los Alimentos, Consejo Superior de Investigaciones Científicas, E-46100 Burjassot, Valencia, Spain.
Appl Environ Microbiol. 2007 Jan;73(1):110-6. doi: 10.1128/AEM.01360-06. Epub 2006 Oct 27.
Unsaturated fatty acids play an essential role in the biophysical characteristics of cell membranes and determine the proper function of membrane-attached proteins. Thus, the ability of cells to alter the degree of unsaturation in their membranes is an important factor in cellular acclimatization to environmental conditions. Many eukaryotic organisms can synthesize dienoic fatty acids, but Saccharomyces cerevisiae can introduce only a single double bond at the Delta(9) position. We expressed two sunflower (Helianthus annuus) oleate Delta(12) desaturases encoded by FAD2-1 and FAD2-3 in yeast cells of the wild-type W303-1A strain (trp1) and analyzed their effects on growth and stress tolerance. Production of the heterologous desaturases increased the content of dienoic fatty acids, especially 18:2Delta(9,12), the unsaturation index, and the fluidity of the yeast membrane. The total fatty acid content remained constant, and the level of monounsaturated fatty acids decreased. Growth at 15 degrees C was reduced in the FAD2 strains, probably due to tryptophan auxotrophy, since the trp1 (TRP1) transformants that produced the sunflower desaturases grew as well as the control strain did. Our results suggest that changes in the fluidity of the lipid bilayer affect tryptophan uptake and/or the correct targeting of tryptophan transporters. The expression of the sunflower desaturases, in either Trp(+) or Trp(-) strains, increased NaCl tolerance. Production of dienoic fatty acids increased the tolerance to freezing of wild-type cells preincubated at 30 degrees C or 15 degrees C. Thus, membrane fluidity is an essential determinant of stress resistance in S. cerevisiae, and engineering of membrane lipids has the potential to be a useful tool of increasing the tolerance to freezing in industrial strains.
不饱和脂肪酸在细胞膜的生物物理特性中起着至关重要的作用，并决定了膜附着蛋白的正常功能。因此，细胞改变其膜中不饱和程度的能力是细胞适应环境条件的一个重要因素。许多真核生物能够合成二烯酸脂肪酸，但酿酒酵母只能在Δ(9)位置引入一个双键。我们在野生型W303-1A菌株（trp1）的酵母细胞中表达了由FAD2-1和FAD2-3编码的两种向日葵（Helianthus annuus）油酸Δ(12)去饱和酶，并分析了它们对生长和胁迫耐受性的影响。异源去饱和酶的产生增加了二烯酸脂肪酸的含量，尤其是18:2Δ(9,12)、不饱和指数以及酵母膜的流动性。总脂肪酸含量保持不变，单不饱和脂肪酸水平降低。FAD2菌株在15℃下的生长受到抑制，这可能是由于色氨酸营养缺陷，因为产生向日葵去饱和酶的trp1（TRP1）转化体与对照菌株生长情况相同。我们的结果表明，脂质双层流动性的变化会影响色氨酸的摄取和/或色氨酸转运体的正确靶向。在Trp(+)或Trp(-)菌株中，向日葵去饱和酶的表达均增加了对NaCl的耐受性。二烯酸脂肪酸的产生增加了在30℃或15℃下预孵育的野生型细胞对冷冻的耐受性。因此，膜流动性是酿酒酵母抗逆性的一个重要决定因素，膜脂工程有可能成为提高工业菌株冷冻耐受性的一种有用工具。
