Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 279, Issue 43, Pages 44683-44689Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M401583200
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Phosphatidylinositol (PtdIns) phosphate (PtdInsP) lipids are used as intracellular signposts for the recruitment and activation of peripheral membrane proteins. Whereas the distribution of most PtdInsPs is restricted to a single organelle, PtdIns(4)P is unique in that it exists in several discrete pools, and so proteins that bind PtdIns(4) P must use extra receptors to achieve a restricted localization. Here we compare the two highly related pleckstrin homology (PH) domains from Osh1p and Osh2p, yeast homologues of oxysterol-binding protein (OSBP), that target membranes using PtdIns(4) P, and in vitro bind both PtdIns(4) P and PtdIns(4,5) P(2). We show that Golgi targeting is specified by an additional site on PH(Osh1), which lies on a face of the domain not previously known to interact with receptors. In contrast, PH(Osh2) does not have a demonstrable second site, and targets multiple pools of PtdInsPs, each dependent on a different PtdIns 4-kinase. This lack of a second site in PH(Osh2) allows it to be used as an unbiased reporter for altered distribution of 4-phosphorylated PtdIns. For example, in cells with excess PtdIns(4) P caused by inactivation of the phosphatase Sac1p, PH(Osh2) indicates that PtdIns(4) P accumulates on the plasma membrane, whereas other Golgi-targeted PH domains fail to detect this change.
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