The Spo7 sequence LLI is required for Nem1-Spo7/Pah1 phosphatase cascade function in yeast lipid metabolism.

Area of Science:

• Biochemistry
• Molecular Biology
• Yeast Genetics

Background:

• The Nem1-Spo7 complex is a vital protein phosphatase in *Saccharomyces cerevisiae*.
• It dephosphorylates Pah1 phosphatidate phosphatase, regulating its membrane translocation.
• This complex is central to triacylglycerol and phospholipid synthesis.

Purpose of the Study:

• To identify specific residues in Spo7 that mediate Nem1-Spo7 complex formation.
• To understand the role of Spo7 in the catalytic function of the Nem1-Spo7 complex.
• To elucidate the impact of Spo7 mutations on the Nem1-Spo7/Pah1 pathway.

Main Methods:

• Deletion analysis of the Spo7 protein.
• Site-directed mutagenesis of identified Spo7 residues (LLI sequence).
• Phenotypic analysis of *spo7*Δ mutant strains and complemented strains.

Main Results:

• A hydrophobic Leu-Leu-Ile (LLI) sequence (residues 54-56) in Spo7 was identified as essential for complex formation and function.
• Mutational analysis confirmed that the hydrophobicity of the LLI sequence is critical for Nem1-Spo7 complex assembly and Pah1 dephosphorylation *in vivo*.
• Spo7 LLI mutations impacted lipid synthesis, lipid droplet formation, and membrane morphology, consistent with disruption of the Nem1-Spo7/Pah1 axis.

Conclusions:

• The hydrophobicity of the Spo7 LLI sequence is a key determinant for Nem1-Spo7 complex formation.
• This complex plays a critical role in regulating Pah1 phosphatidate phosphatase activity.
• The findings provide insights into the molecular mechanisms governing lipid metabolism and cellular processes regulated by this phosphatase cascade.