Sec14
Inositol lipids have specialized functions in eukaryotic organisms. Not only do they provide a source of second messengers but they are also recognized as signaling molecules. Moreover, inositol lipids are required as substrates for PLC and PI3K activities, as well as having a role in cytoskeletal reorganization and vesicular traffic. The cytosolic protein Phosphatidylinositoltransfer protein (PITP) is a key regulator of the cellular mechanism that can compartmentalize the synthesis of these phosphoinositides[1]. PIPTs mediate the transfer of monomeric phosphatidylinositol (PI) or phosphatidylcholine (PC) molecules between two membrane compartments of a cell. Sec14p is a PIPT found in yeast, and is the prototype for a protein module called the SEC14 domain. SEC14 domains are found in proteins from plants, yeast, invertebrates, and mammals (named CRAL_TRIO domain), suggesting an ancient evolutionary origin. Many proteins with a SEC14 domain consist only of this module, while others are larger proteins with additional protein–protein interaction or catalytic domains. It appears likely that the SEC14-only proteins are bona fide lipid transport proteins, while the multi-domain SEC14-containing proteins have more complex functions in signal transduction, transport, and organelle biology, where they integrate lipid metabolism with other biochemical processes[2]. Abberant functioning of SEC14, either due to individual deficiencies, genetic mutations or chemical inhibition, impairs cell viability through compromised Phosphatidylinositol (PtdIns) trafficking through the trans-Golgi network (TGN) and endosomal systems, phosphatidylserine decarboxylation to phosphatidylethanolamine, fatty acid metabolism, polarized growth, and fungal dimorphism. Mutations in PITPs, or PITP-like proteins, are also root causes of mammalian neurodegenerative and lipid homeostatic diseases[3].
[1] S. Cockcroft. Phosphatidylinositol transfer proteins: a requirement in signal transduction and vesicle traffic. Bioessays. 1998 May;20(5):423-32.
[2] K. Saito et al. The lipid-binding SEC14 domain. Biochim Biophys Acta. 2007 Jun;1771(6):719-26.
[3] A.H. Nile et al. PITPs as targets for selectively interfering with phosphoinositide signaling in cells. Nat Chem Biol. 2014 Jan;10(1):76-84.