title: Glycolipid transfer protein mediated transfer of glycosphingolipids between membranes: a model for action based on kinetic and thermodynamic analyses.
abstract: Glycolipid transfer protein (GLTP) catalyzes the intermembrane transfer of lipids that have sugars beta-linked to either diacylglycerol or ceramide backbones, including simple glycosphingolipids (GSLs) and gangliosides. The present study provides a quantitative understanding of GLTP action involving bilayer vesicles that have high and low curvature stress, i.e., small and large unilamellar vesicles (SUVs and LUVs). When the GSL intervesicular transfer was monitored in real time using an established fluorescence resonance energy approach, the initial GSL transfer rates (v(0)) and net transfer equilibrium (K(eq)) were determined for GLTP-mediated transfer from SUVs and LUVs over the temperature range of 30-44 degrees C. v(0) exhibited a linear dependence with respect to varying GLTP concentrations (0-143 nM range) in SUVs and LUVs, suggesting a first order dependence on the GLTP bulk concentration. Thermodynamic parameters associated with the GLTP-GSL transition-state complex and GSL net transfer were determined from linear Arrhenius and van't Hoff plots, respectively. Although initial transfer rates were lower for LUVs than for SUVs, the activation energy barriers were higher for LUVs, while the Gibbs's free energy of the transition states were similar. The formation of a transition-state complex was predominantly enthalpy driven, whereas the net transfer of GSLs was mainly entropy driven. The rate-limiting step for GLTP action appeared to be the surface processes leading to the GLTP-GSL complex formation and release associated with a shuttle/carrier mode of action. Because surface processes leading to the GLTP-GSL complex formation were limiting for GLTP action with SUVs and LUVs, it was concluded that GLTP is likely to be a valuable tool to probe and manipulate GSL environments in membranes.
authors.affiliation: The Hormel Institute, University of Minnesota, 801 16th Avenue Northeast, Austin, Minnesota 55912-3698, USA. chetan@hi.umn.edu
authors.forename: Chetan S
authors.initials: CS
authors.lastname: Rao
authors.forename: Xin
authors.initials: X
authors.lastname: Lin
authors.forename: Helen M
authors.initials: HM
authors.lastname: Pike
authors.forename: Julian G
authors.initials: JG
authors.lastname: Molotkovsky
authors.forename: Rhoderick E
authors.initials: RE
authors.lastname: Brown
mesh_terms: D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D002417:Cattle; D005699:Galactosylceramides / Q000737:chemistry / Q000378:metabolism; D006028:Glycosphingolipids / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D008081:Liposomes; D021962:Membrane Microdomains / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D008956:Models, Chemical; D008969:Molecular Sequence Data; D010713:Phosphatidylcholines / Q000737:chemistry / Q000378:metabolism; D011609:Psychosine / Q000737:chemistry / Q000378:metabolism; D013499:Surface Properties; D013552:Swine; D013696:Temperature; D013816:Thermodynamics
chemical_list: D002352:Carrier Proteins; C511922:GLTP protein, human; D005699:Galactosylceramides; C511923:Gltp protein, mouse; D006028:Glycosphingolipids; D008051:Lipid Bilayers; D008081:Liposomes; D010713:Phosphatidylcholines; C030363:lipid transfer protein; D011609:Psychosine; C028694:1-palmitoyl-2-oleoylphosphatidylcholine