Yeast phosphatidylinositol transfer protein Pdr17 does not require high affinity phosphatidylinositol binding for its...

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Yeast phosphatidylinositol transfer protein (PITP) Pdr17 is essential for phosphatidylserine (PS) decarboxylation to phosphatidylethanolamine (PE).
• This process occurs at a non-mitochondrial location, involving PS transfer from the endoplasmic reticulum to the Golgi/endosomes.

Purpose of the Study:

• To investigate the mechanism of Pdr17p in PS decarboxylation by generating and analyzing a Pdr17^{E237A, K269A} mutant.
• To elucidate the role of phosphatidylinositol (PI) binding in Pdr17p's cellular functions.

Main Methods:

• Generation of a Pdr17^{E237A, K269A} mutant protein.
• Assays using permeabilized human cells to assess PI binding.
• In vitro assays to evaluate inter-membrane PI transfer.
• Molecular modeling to analyze mutation effects on protein structure.

Main Results:

• The Pdr17^{E237A, K269A} mutant lost the ability to bind PI in human cells but retained in vitro PI transfer capacity.
• Molecular models indicated mutations affected the PI binding cavity, not surface properties.
• PI binding is not essential for Pdr17p's primary role in PS transfer, unlike its homolog Pdr16p.

Conclusions:

• Yeast PITPs Pdr16p and Pdr17p likely evolved from a common ancestor with divergent functions.
• Pdr16p requires PI binding for its roles, whereas Pdr17p has adapted to a function independent of high-affinity PI binding.
• PITP functions are complex in vivo, necessitating consideration of multiple parameters beyond lipid binding for in vitro studies.