Assembly of protein structures on liposomes by non-specific and specific interactions

We investigate different schemes for fabrication of nanometer sized assemblies that consist of a liposome core over which a shell of ferritin is attached. Three distinct interactions were used for this assembly: (i) Electrostatic attraction. The liposomes are charged by the presence of cationic surfactant (HTAB) and at an appropriate pH collect the ferritin molecules into a 2D-ordered ferritin shell. The protein shells can be fixed by glutaraldehyde. Next, the liposomes can be removed by solubilisation, leaving behind ordered ferritin clusters. (ii) Specific avidin-biotin or streptavidin-biotin binding. The ferritin molecules are conjugated to avidin or streptavidin and the liposomes incorporate biotinylated lipid. We found that the specific binding can be completely blocked by unfavourable electrostatic repulsion. To adjust the appropriate liposome charge we include cationic surfactant in the lipid layer. Thus, to accomplish the assembly process, we need to design and modify both the specific and non-specific colloid interactions in the system. The result is liposomes heavily coated with a strongly and specifically attached ferritin layer. (iii) Specific polysaccharide/lectin binding. The liposomes are first coated with a cholesterol-anchored mannan layer. The ferritin molecules are conjugated with Con A that binds to the polysaccharide. A smooth and dense coating with ferritin is obtained (Fig. 3b). The acquired data can find application in the future fabrication of microstructured, multicomponent, or functionalised protein and liposome/ protein assemblies.