Crystallization and preliminary X-ray diffraction studies of the Saccharomyces cerevisiae phospholipid-transfer...

The Saccharomyces cerevisiae phosphatidylinositol-transfer protein Secl4p 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 Sec 14p translates to in vivo function. In an attempt to determine the structural basis for how Secl4p binds each of its phopholipid ligands, Secl4p occupied with phosphatidylcholine has been purified and the complex crystallized in the presence of the mild detergent n-octyl beta-D-glucopyranoside. The Secl4p crystals diffract to 2.7 A and belong to space group P3(1)21 or P3(2)21 with unit-cell dimensions of a = b = 88.79, c = 111.21 A, alpha = beta = 90, gamma = 120 degrees. As Secl4p 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 Secl4p crystal structure will provide new functional insights for a family of interesting proteins.