Abstract
Lipid transfer proteins (LTPs) are emerging as key players in lipid homeostasis by mediating non-vesicular transport steps between two membrane surfaces. Little is known about the driving force that governs the direction of transport in cells. Using the soluble LTP glycolipid transfer protein (GLTP), we examined GM1 (monosialotetrahexosyl-ganglioside) transfer to native membrane surfaces. With artificial GM1 donor liposomes, GLTP can be used to increase glycolipid levels over natural levels in either side of the membrane leaflet, i.e., external or cytosolic. In a system with native donor- and acceptor-membranes, we find that GLTP balances highly variable GM1 concentrations in a population of membranes from one cell type, and in addition, transfers lipids between membranes from different cell types. Glycolipid transport is highly efficient, independent of cofactors, solely driven by the chemical potential of GM1 and not discriminating between the extra- and intracellular membrane leaflet. We conclude that GLTP mediated non-vesicular lipid trafficking between native membranes is driven by simple thermodynamic principles and that for intracellular transport less than 1 µM GLTP would be required in the cytosol. Furthermore, the data demonstrates the suitability of GLTP as a tool for artificially increasing glycolipid levels in cellular membranes.
Highlights
Plasmalemmal and intracellular membranes vary in their unique protein and lipid compositions [1,2]
Native membranes have a large capacity for taking up additional glycolipids albeit it cannot be excluded that due to the broad specificity of glycolipid transfer protein (GLTP) for glycolipids the increase reflects in part exchange of glycolipids by GM1
Our study shows that GLTP readily inserts GM1 from liposomes into both leaflets of a native plasma membrane, demonstrating that membrane crowding does not preclude efficient transfer cycles
Summary
Plasmalemmal and intracellular membranes vary in their unique protein and lipid compositions [1,2]. It is assumed that metabolism and vesicle trafficking generate the observed membrane diversity and control lipid homeostasis. Lipid transfer proteins (LTPs) have emerged as novel key players mediating non-vesicular lipid transport steps [3,4,5]. LTPs can be genetically classified or functionally sub-divided into three major groups: phospholipid-, sterol- and sphingolipidtransfer proteins [4]. All LTPs contain a lipid binding domain and often additional motifs for subcellular targeting. The lipid binding domain is able to recognize several related lipids. Though LTPs have an intrinsic lipid transfer activity, some of them might play a role as lipid sensor [6,7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
