Sterol synergism in yeast

Area of Science:

• Molecular Biology
• Biochemistry
• Yeast Genetics

Background:

• Sterol synergism, defined as a greater-than-additive growth response to pairs of sterols, was previously observed in Mycoplasma capricolum.
• Yeast mutant GL7 is auxotrophic for sterol and unsaturated fatty acid, requiring specific sterol supplementation for growth.

Purpose of the Study:

• To demonstrate sterol synergism in the yeast mutant GL7.
• To investigate the metabolic role of ergosterol in yeast membranes.

Main Methods:

• Supplementation of yeast mutant GL7 with various sterols (cholesterol, ergosterol, stigmasterol, 7-dehydrocholesterol) and oleic acid.
• Measurement of cell growth rates and yields.
• Incorporation of [1-14C]oleic acid into phospholipids in cells grown under different sterol conditions.

Main Results:

• Yeast mutant GL7 exhibited pronounced increases in growth rates and cell yields when supplemented with ergosterol (1:3 ergosterol-to-cholesterol ratio).
• Stigmasterol and 7-dehydrocholesterol also showed synergistic effects, though less pronounced than ergosterol.
• Cells grown on an ergosterol-cholesterol mixture incorporated oleic acid into phospholipids at significantly faster rates compared to cells grown on cholesterol alone.

Conclusions:

• Sterol synergism is demonstrated in the yeast mutant GL7, highlighting ergosterol's significant role.
• Ergosterol plays a crucial metabolic role in yeast membranes, influencing phospholipid synthesis and fatty acid incorporation.