Activity of phosphatidylinositol transfer protein is sensitive to ethanol and membrane curvature

Abstract

Phosphatidylinositol transfer protein (PITP) is critical for many cellular signalling and trafficking events that are influenced by ethanol. The influence of ethanol and membrane curvature on the activity of recombinant mouse PITP-α in vitro is evaluated by monitoring the transfer of phosphatidylinositol (PtdIns) from rat hepatic microsomes to unilamellar vesicles. Acute exposure to pharmacological levels of ethanol enhanced the function of PITP. Chloroform shared a similar ability to enhance function when both drug concentrations were normalized to their respective octanol/water partition coefficients, indicating that the effect is not unique to ethanol and might be common to hydrophobic solutes. Neither the PITP activity nor its ethanol enhancement was altered by using thermally pretreated (denatured) or protease-treated microsomes, indicating that the native microsomal protein structure was unlikely to be a determinant of transfer. Kinetic analyses indicated that ethanol acted by increasing the PITP-mediated flux of PtdIns from both microsomal and liposomal surfaces. The activity of PITP was strongly dependent on the lipid structure, with a steep dependence on the expressed curvature of the membrane. Activity was greatest for small, highly curved sonicated vesicles and decreased markedly for large, locally planar unilamellar vesicles. Ethanol enhanced PITP-mediated PtdIns transfer to all vesicles, but its effect was much smaller than the enhancement due to curvature, which is consistent with ethanol's comparatively modest ability to perturb membrane lipids. The ethanol efficacy observed is as pronounced as any previously described lipid-mediated ethanol action. In addition, these observations raise the possibility that PITP specifically delivers PtdIns to metabolically active membrane domains of convex curvature and/or low surface densities of lipid.

Membrane lipids and cell death: an overview

“…Hence, Bid and Bax may respond not only to chemical but also physical properties of lipid membranes, in particular bilayer curvature (Basanez et al, 2002;Epand et al, 2002b). Of note, PI-transfer protein and other lipid transporters are also sensitive to bilayer curvature in their interaction with membranes (Tremblay et al, 1996;Komatsu et al, 2000;Degli Esposti, 2002c). Bid has a strong affinity for several lysolipids , in analogy with plant lipid transfer proteins (LTP; Gomar et al, 1996).…”

Role of cholesteryl ester transfer protein in selective uptake of high density lipoprotein cholesteryl esters by adipocytes

“…Alternatively, CETP may transfer lipids to particular membrane structures such as microvilli or protrusions (46) that have a high curvature and therefore may, at a molecular level, be comparable to a lipoprotein. The transfer activity of other lipid transfer proteins (PL transfer protein and phosphatidylinositol transfer protein) has been positively correlated with high bilayer curvature (47,48), but data for CETP are lacking.…”

Mechanism underlying bupivacaine inhibition of G protein-gated inwardly rectifying K + channels

“…Ethanol may enhance the interaction of PIP 2 with GIRK channels. Alternatively, ethanol has been reported to increase the activity of phosphatidylinositol transfer protein, which could increase the levels of PIP 2 (52). Ethanol may not activate ROMK (Kir1) and IRK (Kir2) channels because of their high affinity for PIP 2 .…”