Fusion and Steric Stabilization of Liposomes Containing Membrane-Anchored Biopolymers

Abstract

<p> Studies examining the characteristics of membranes that facilitate and affect fusion are central to understanding the intricacies of inter- and intra-cellular fusion processes and expanding the existing knowledge of other roles membranes may have. In this thesis a model membrane system, using Sendai Virus and Egg phosphatidylcholine (EggPC) liposomes containing the receptor glycophorin A (proteoliposomes), was used in examining different fusion with proteoliposomes prepared by different methods. For the first time glycophorin A was incorporated into EggPC liposomes vectorially. This was accomplished separately with two detergents: octylglucoside and CHAPS. Fusion of Sendai Virus with the reconstituted proteoliposomes revealed that octylglucoside reconstituted proteoliposomes exhibited lower fusion compared with CHAPS reconstituted proteoliposomes. Efforts to determine the basis for this difference, using either proteinase K or O-glycosidase digestion and subsequent fragment analysis using SDS-PAGE and silver-staining, were inconclusive. A separate study examined the ability of large membrane-anchored biopolymers (chosen in virtue of their large hydrophilic domains) to sterically stabilize Egg PC liposomes. Glycophorin A, the lipophosphoglycan (LPG) from Leishmania donovani, and a polyethyleneglycol-conjugated phospholipid (PEG5000-PE) were incorporated into Egg PC liposomes. In each case, binding of a soluble fluorescent probe, NeutrAvidin Oregon Green, to liposomes containing biotin-conjugated lipid was restricted. This supports the idea that large membrane-anchored biopolymers are able to sterically stabilize liposomes.</p>