Polyhistidine mediates an aicd [sic] dependent fusion of negatively charged liposomes

Author

Chen-Yen Wang

Date of Award

3-1984

Degree Type

Thesis

Degree Name

Master of Science

Major

Biochemistry and Cellular and Molecular Biology

Major Professor

Leaf Huang

Abstract

Polyhistidine facilitates the fusion of negatively charged liposomes prepared by sonication. Liposome fusion was demonstrated by (a) negative stain electron microscopy, (b) gel filtration and (c) resonance energy transfer of the fluorescent phospholipids. Liposome fusion required the presence of polyhistidine, whereas histidine at equivalent concentrations had no effect. Little or no liposome fusion was detectable at pH 7.4, but it was greatly enhanced when the pH of medium was reduced below 6.5. Although acidic phospholipid is necessary for fusion, liposomes made of acidic lipids alone showed only low levels of fusion activity. Liposomes composed of mixtures (1:1) of a negatively charged phospholipid and a neutral phospholipid such as phosphatidylcholine, phosphatidylethanolamine, but not sphingomyelin, showed high levels (about 80%) of fusion competency. For liposomes made of PE/PS (1:1), fusion at pH 5.2 and 2.5 g/ml of polyhistidine resulted in an increase in the average liposome diameter from 300 to 2,400 A, indicating multiple rounds of fusion had occurred. Liposome fusion was not very leaky as revealed by the lack of release of encapsulated calcein. For PE/PS (1:1) liposomes, about 10% of dye leakage was observed for up to about 30% liposome fusion and about 45% leakage at 80% liposome fusion. Since polyhistidine becomes a strong polycation at acidic pH, liposome fusion may be a direct result of the bilayer phase separation induced by the binding of polyhistidine with the negatively charged phospholipids. Therefore, this phenomenon is similar to the liposome fusion induced by other polycations such as polylysine at neutral pH. This system may serve as a model for studies on the acid dependent fusion of viral envelopes with target cell membranes, such as in the case of the Influenza, Vesicular Stomatitis and Semliki Forest Viruses.

Recommended Citation

Wang, Chen-Yen, "Polyhistidine mediates an aicd [sic] dependent fusion of negatively charged liposomes. " Master's Thesis, University of Tennessee, 1984.
https://trace.tennessee.edu/utk_gradthes/14736