Phosphoinositide Signaling Meets Heme Biochemistry

The Phosphatidylinositol Transfer Proteins (PITPs) have emerged as central regulators of phosphoinositide signaling that that diversify signaling outcomes in cells. Sec14 is the prototype PITP in S. cerevisiae with five homologs (Sfh1‐Sfh5) involved in activities as diverse as trans‐ Golgi signaling and lipid droplet metabolism to phosphatidylethanolamine and ergosterol metabolism. Sfh5 is an orphan member of this family with unknown function with limited information about its genetic interactions or chemogenomic signatures. The surface potential map of Sfh5 indicated unusual electrostatics in the lipid‐binding domain of the protein. We purified recombinant Sfh5 protein from E. coli and subjected it to rigorous biochemical and biophysical analysis. We show that Sfh5 is a heme binding protein with a high spin ferric center as characterized by EPR and Mössbauer Spectroscopy. We solved the crystal structure of the heme‐bound protein to 2.6Å resolution and show that the lipid binding and heme binding sites overlap. We also identified a novel heme‐coordination motif that is conserved through fungal Sfh5s. Finally, we show that the lipid transfer ability of Sfh5 is enhanced when the protein is stripped of heme. We speculate that this protein is a heme‐transfer protein that delivers hemes within cell, particularly under conditions of oxidative stress. Taken together, this is for the first time phosphoinositide signaling proteins have been linked with bioinorganic chemistry involving heme. Support or Funding Information This work was funded in part by a grant from the National Institutes of Health (GM44530) and by the Robert A. Welch Foundation (BE0017). This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .