Devising powerful genetics, biochemical and structural tools in the functional analysis of phosphatidylinositol...

The minor cellular lipid phosphoinositides represents key regulators of diverse intracellular processes such as signal transduction at membrane-cytosol interface, regulation of membrane trafficking, cytoskeleton organization, nuclear events and the permeability, and transport functions of the membrane. The heterogeneous subcellular localization of phosphoinositides and their multiple and co-operative membrane-protein recognition mechanisms contribute to a "coincidence detection code" for the membrane-cytosol interactions in eukaryotic signaling networks. Such a "coincidence detection code" relies on the fine coordination of the broader lipid metabolism and organization, and their coupling to dedicated physiological processes. The phosphatidylinositol transfer proteins (PITPs) play a key regulatory role, essentially as "coincidence detectors" or "nanoreactors" in this "signal detection code" that spatially and temporally coordinate the diverse aspects of lipid metabolome with phosphoinositide signaling to effect various cellular functions. The integral role of PITPs in the highly conserved eukaryotic signal transduction strategy is amply demonstrated by the mammalian diseases associated with the derangements in the function of these proteins, to stress response and developmental regulation in plants, to fungal dimorphism and pathogenicity, to membrane trafficking in yeast and higher eukaryotes. The study of PITPs is fundamental to understanding of how the phosphoinositide signal transduction network is regulated and integrated to the larger lipid metabolome in diverse cellular processes. To comprehend how the PITPs integrate phosphoinositide signaling to broader lipid metabolome in diverse cellular processes, it is necessary to devise methods that can correlate the biochemical properties of these non-enzymatic proteins to biologically relevant functional insights. In this chapter, we present combinatorial approaches that primarily employ genetics and structural tools to assess the functional role of PITPs in yeast, plant and mammalian systems. An elaborate discussion on the various genetic models devised for interpreting the functional role of PITPs in relation to their operational assays has been included. We also describe the structural and biophysical methods that have advanced our understanding of how these proteins operate as "nanoreactor" molecules.