Atomic force microscopy of liposomes bearing fibrinogen

Extruded liposomes formed from dipalmitoylphosphatidylcholine and cholesterol, with and without fibrinogen, were examined by atomic force microscopy (AFM). The sequence of events involved in the transition from attached liposomes to bilayer patches on mica supports was viewed by tapping mode in liquid. After adhesion to the mica surface, both liposomes without fibrinogen and liposomes with attached fibrinogen collapsed into patches. The fibrinogen layer attached to the liposomes was 2.6 nm thick. This implied that the protein was spread over the entire liposome and the protein characteristic trinodular structure disappeared. To check the type of bond between fibrinogen and liposome, sequential images were taken after the incubation of fibrinogen with liposomes with and without a chemical group for attaching the protein. The results clearly confirmed that fibrinogen bound covalently to liposomes.