Abstract
Lipid rafts are liquid-ordered membrane microdomains that form by preferential association of 3-β-hydroxysterols, sphingolipids and raft-associated proteins often having acyl modifications. We isolated lipid rafts of the protozoan parasite Trypanosoma brucei and determined the protein composition of lipid rafts in the cell. This analysis revealed a striking enrichment of flagellar proteins and several putative signaling proteins in the lipid raft proteome. Calpains and intraflagellar transport proteins, in particular, were found to be abundant in the lipid raft proteome. These findings provide additional evidence supporting the notion that the eukaryotic cilium/flagellum is a lipid raft-enriched specialized structure with high concentrations of sterols, sphingolipids and palmitoylated proteins involved in environmental sensing and cell signaling.
Highlights
Cell membranes constitute a large fraction of the biomass of a typical cell and contain 25–40%of all cellular proteins [1]
The lipid raft preparation was applied to a discontinuous Optiprep gradient and gradient fractions were analyzed by SDS-PAGE and western blotting for Calflagin, a well-characterized family of three flagellar calcium binding proteins (Tb44, Tb24 and Tb17) that associate with lipid rafts [4] via dual acylation with myristate and palmitate [12]
The lipid raft fractions contain the raft-associated protein CAP5.5 [24] but do not contain mitochondrial Hsp70, which is found in the mitochondrial matrix (Figure 1B)
Summary
Cell membranes constitute a large fraction of the biomass of a typical cell and contain 25–40%of all cellular proteins [1]. Cell membranes constitute a large fraction of the biomass of a typical cell and contain 25–40%. The lipid modifications include glycosylphosphatidylinositol anchors, N-terminal myristic acid tails, palmitic acid tails acquired through cysteine acylation, and C-terminal prenyl groups. Within cell membranes are microdomains called lipid rafts, which are liquid-ordered (gel-like) regions containing high concentrations of 3-β-hydroxysterols, sphingolipids and proteins having acyl modifications such as myristoylation and palmitoylation [2,3,4,5]. Lipid rafts are present in all eukaryotic cells and provide platforms for the assembly of cell-signaling complexes [2,6,7]. Lipid rafts have the special property of detergent resistance and can be extracted from the membrane using cold non-ionic detergents [6]. Lipid rafts or raft-associated proteins are involved in the pathogenesis of a number of human diseases, including infectious diseases [8]
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