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A Sec14-like Phosphatidylinositol Transfer Protein Paralog Defines a Novel Class of Heme-binding Proteins With An Unusual Heme Coordination Mechanism

By Danish Khan, Dongju Lee, Gulcin Gulten, Anup Aggarwal, Joshua Wofford, Inna Krieger, Ashutosh Tripathi, John W. Patrick, Debra M Eckert, Arthur Laganowsky, James Sacchettini, Paul Lindahl, Vytas A. Bankaitis

Posted 20 Mar 2020
bioRxiv DOI: 10.1101/2020.03.19.999003 (published DOI: 10.7554/eLife.57081)

Yeast Sfh5 is an unusual member of the Sec14-like phosphatidylinositol transfer protein (PITP) family. Whereas PITPs are defined by their abilities to transfer phosphatidylinositol between membranes in vitro, and to stimulate phosphoinositide signaling in vivo, Sfh5 does not exhibit these activities. Rather, Sfh5 is a redox-active penta-coordinate high spin FeIII heme-binding protein with an unusual heme-binding arrangement that involves a co-axial tyrosine/histidine coordination strategy and a complex electronic structure connecting the open shell iron d-orbitals with three aromatic ring systems. That Sfh5 is not a PITP is supported by demonstrations that heme is not a readily exchangeable ligand, and that phosphatidylinositol-exchange activity is resuscitated in heme binding-deficient Sfh5 mutants. The collective data identify Sfh5 as the prototype of a new class of fungal hemoproteins, and emphasize the versatility of the Sec14-fold as scaffold for translating the binding of chemically distinct ligands to the control of diverse sets of cellular activities.

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