Endocytic Sorting of Lipid Analogues Differing Solely in the Chemistry of Their Hydrophobic Tails

Abstract

To understand the mechanisms for endocytic sorting of lipids, we investigated the trafficking of three lipid-mimetic dialkylindocarbocyanine (DiI) derivatives, DiIC16(3) (1,1′-dihexadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate), DiIC12(3) (1,1′- didodecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate), and FAST DiI (1,1′-dilinoleyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate), in CHO cells by quantitative fluorescence microscopy. All three DiIs have the same head group, but differ in their alkyl tail length or unsaturation; these differences are expected to affect their distribution in membrane domains of varying fluidity or curvature. All three DiIs initially enter sorting endosomes containing endocytosed transferrin. DiIC16(3), with two long 16-carbon saturated tails is then delivered to late endosomes, whereas FAST DiI, with two cis double bonds in each tail, and DiIC12(3), with saturated but shorter (12-carbon) tails, are mainly found in the endocytic recycling compartment. We also find that DiOC16(3) (3,3′- dihexadecyloxacarbocyanine perchlorate) and FAST DiO (3,3′-dilinoleyloxacarbocyanine perchlorate) behave similarly to their DiI counterparts. Furthermore, whereas a phosphatidylcholine analogue with a BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) fluorophore attached at the end of a 5-carbon acyl chain is delivered efficiently to the endocytic recycling compartment, a significant fraction of another derivative with BODIPY attached to a 12-carbon acyl chain entered late endosomes. Our results thus suggest that endocytic organelles can sort membrane components efficiently based on their preference for association with domains of varying characteristics.

CD1 Molecules Efficiently Present Antigen in Immature Dendritic Cells and Traffic Independently of MHC Class II During Dendritic Cell Maturation

“…Unlike other CD1 molecules, CD1a lacks the cytoplasmic tail tyrosine-based sorting sequence, and, within the endocytic system, is expressed solely in early endosomes of the recycling pathway (18). Together, these observations underscore the capacity of CD1 to broadly survey the endocytic system for sampling lipid Ags that may localize in various endocytic subcompartments (19).…”

Bacterial protein toxins and lipids: role in toxin targeting and activity

“…Indeed, lipid rafts with long and saturated fatty acids are preferentially targeted to late endosomes/lysosomes, whereas those with short and unsaturated fatty acid chains are preferentially transported to the endocytic/recycling endosome compartment. Lipid shape and fluidity preference, according to length and degree of saturation of acyl chains, appear to be critical in lipid sorting that probably results from preferential partitioning in more fluid or more rigid regions of the bilayer (Mukherjee et al, 1999;Fivaz et al, 2002).…”

Down-Regulation of Cell Surface Receptors Is Modulated by Polar Residues within the Transmembrane Domain

“…Internalized and targeted to lysosomes LTYLGGAVASTTGLEVGGTLLALL (Green et al, 1994) of the lipid hydrophobic tails (Mukherjee et al, 1999). This intriguing study demonstrated that lipids with long (16-carbon) saturated tails are delivered to late endosomes, whereas lipids with two cis double bonds or with saturated but shorter tails (12-carbon) are delivered to the recycling compartment.…”

“…This intriguing study demonstrated that lipids with long (16-carbon) saturated tails are delivered to late endosomes, whereas lipids with two cis double bonds or with saturated but shorter tails (12-carbon) are delivered to the recycling compartment. In their model, Mukherjee et al (1999) propose that lipid trafficking in the endocytic and other pathways depends on differences in fluidity. They suggest that those lipids with long unsaturated tails preferentially partition into domains that are more ordered and unsaturated or shorter tails partition into more fluid regions of the bilayer.…”