Phosphatidylserine synthase from yeast

Area of Science:

• Biochemistry
• Molecular Biology
• Yeast Genetics

Background:

• Mammalian cells synthesize phosphatidylserine (PS) via base exchange.
• Yeast cells utilize a distinct pathway involving PS synthase and CDP-diacylglycerol.
• Understanding yeast PS synthesis is crucial for comparative cell biology.

Purpose of the Study:

• To purify and characterize yeast PS synthase.
• To identify and analyze the gene encoding PS synthase (PSS/CHO1).
• To investigate the regulation of PS synthesis in yeast.

Main Methods:

• Enzyme purification to homogeneity.
• Gene cloning via complementation of auxotrophic mutants.
• Protein sequence analysis and comparison.
• Enzyme activity assays under various conditions.
• Investigating enzyme phosphorylation and inhibition.
• Analysis of gene expression regulation.

Main Results:

• Yeast PS synthase is a 23 kDa enzyme requiring divalent cations and Triton X-100.
• The PSS/CHO1 gene encodes a 30.8 kDa precursor that is processed to the active enzyme.
• The enzyme specifically transfers phosphatidyl groups to L-serine.
• Enzyme activity is regulated by phosphorylation, substrate/product levels, and sphingoid bases.
• Expression is repressed by myo-inositol and choline, involving a specific regulatory DNA sequence.
• Sequence analysis reveals conserved motifs and similarity to bacterial enzymes.

Conclusions:

• Yeast PS synthase is a well-characterized enzyme with unique regulatory features.
• The PSS/CHO1 gene and its regulatory elements provide insights into phospholipid metabolism control.
• Comparative analysis highlights evolutionary divergence in PS synthesis pathways.
• The findings contribute to understanding lipid biosynthesis and cellular regulation in yeast.