The lipid transfer protein PDR16 of the filamentous ascomycete Sordaria macrospora

Pulldown experiments with the Striatin interaction phosphatase and kinase (STRIPAK) component SCI1 identified an orthologue of the yeast PDR16 phosphatidylinositol (PtdIns) transfer protein as a putative target of the STRIPAK complex in S. macrospora.

The S. cerevisiae homolog of the S. macrospora PDR16 protein is predominantly associated with lipid droplets or is localized either to the plasma membrane (PM) or the PM-associated ER. The role of the Pdr16 protein in yeast metabolism is not fully understood. However, the absence of Pdr16p leads to increased susceptibility of yeast cells to azole antifungals, indicating its role in sterol biosynthesis. By regulating the phospholipid/sterol composition of plasma- and endo-membranes, S. macrospora PDR16 may be involved in membrane recruiting of the STRIPAK signaling complex required for hyphal fusion.

Deletion of Smpdr16 in S. macrospora resulted in no obvious changes in growth, fruiting-body morphology or sexual reproduction under regular conditions. Only when grown at decreased temperatures the ΔSmpdr16 mutant displayed a reduced growth rate in comparison to the wt. SmPDR16 is localized at septa and endo-membranes, but localization at the plasma membrane cannot be ruled out.

To examine the functional conservation of PDR16 proteins, we heterologously expressed the S. macrospora pdr16 cDNA in a yeast Δpdr16 mutant and verified that the S. macrospora gene can substitute for the absence of the yeast protein. To address the lipid/sterol binding capacity of PDR16, we will overexpress SmPDR16 in E. coli followed by purification to perform a lipid binding assay in HL60 cells.