Screening effect of PEG on avidin binding to liposome surface receptors

This study investigates the screening effect of poly(ethylene glycol)-phosp holipids (PE-PEG) on the interaction of avidin with PEGylated liposomes con taining surface-bound biotin ligands. The influence of grafting density and lipopolymer chain length is examined. A simple fluorescence assay involvin g a receptor-mediated fluorescence increase of BODIPY-labeled avidin upon b inding to biotinylated lipids is employed to study the screening effect of submicellar concentrations of 1,2-dipalmitoyl-sn-glycero-3-phosphatidyletha nolamine-N-[poly(ethylene glycol)-2000] (PE-PEG(2000)) and 1.2-dipalmitoyl- sn-glycero-3-phosphatidylethanolamine N-[poly(ethylene glycol)-5000] (PE-PE G(5000)) incorporated into 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) liposomes. The results show that incorporation of lipopolymers into DPPC lipid bilayers reduces binding of avidin to the biotinylated liposome s. and it is found that the screening effect of PE-PEG(5000) is stronger th an that for PE-PEG(2000). Thus, the results reveal that both the grafting d ensity and the polymer length of the PE-PEC lipopolymers are of importance for the ability of water-soluble macromolecules to reach the surface of PEG liposomes. Furthermore. it is found that none of the lipopolymers complete ly prevents avidin from reaching the surface-bound biotin ligands. (C) 2001 Elsevier Science B.V. All rights reserved.