Difference in the late ergosterol biosynthesis between yeast spheroplasts and intact cells

Area of Science:

• Biochemistry
• Cell Biology
• Yeast Metabolism

Background:

• Ergosterol is the main sterol in yeast, crucial for membrane function.
• Sterol synthesis involves complex metabolic pathways with multiple enzymatic steps.
• Understanding these pathways is vital for yeast biotechnology and drug development.

Purpose of the Study:

• To compare post-squalene sterol synthesis in intact yeast cells versus spheroplasts.
• To investigate how cell integrity affects ergosterol biosynthesis.
• To identify specific metabolic blocks in yeast spheroplasts.

Main Methods:

• Incubation of intact yeast cells and spheroplasts with radioactive acetate.
• Comparative analysis of sterol intermediates using strains from Saccharomyces cerevisiae, Schizosaccharomyces pombe, and Pichia pastoris.
• Utilizing engineered S. cerevisiae strains with defects in late ergosterol synthesis.

Main Results:

• Intact cells completed ergosterol synthesis, while spheroplasts showed upstream pathway stalling.
• Accumulation of non-cyclic triterpenes (squalene, oxidosqualene) occurred in spheroplasts.
• Defects in 3-ketosteroid reductase or oxidosqualene cyclase further elucidated pathway differences.

Conclusions:

• Yeast spheroplasts exhibit distinct post-squalene sterol synthesis compared to intact cells, likely due to their non-proliferating state.
• Metabolic pathway stalling in spheroplasts offers insights into yeast metabolic networks.
• Further research into spheroplast metabolic blocks could reveal novel aspects of yeast sterol biosynthesis.