The Saccharomyces cerevisiae phosphatidylinositol-transfer protein Sec14p catalyzes the exchange of phosphatidylinositol or phosphatidylcholine between membrane bilayers in vitro, and is an essential protein required for the budding of secretory vesicles from the yeast Golgi complex in vivo. At issue is the fundamental question of how the dual phospholipid ligand specificity of Sec14p translates to in vivo function. In an attempt to determine the structural basis for how Sec14p binds each of its phopholipid ligands, Sec14p occupied with phosphatidylcholine has been purified and the complex crystallized in the presence of the mild detergent n-octyl β-D-glucopyranoside. The Sec14p crystals diffract to 2.7 Å and belong to space group P3121 or P3221 with unit-cell dimensions of a = b = 88.79, c = 111.21 Å a = β = 90, γ = 120°. As Sec14p exhibits significant primary sequence homology to mammalian retinaldehyde binding proteins and the noncatalytic domain of human MEG2 protein tyrosine phosphatase, is is anticipated that solution of the Sec14p crystal structure will provide new functional insights for a family of interesting proteins.
