The complexation between holothurian triterpene glycosides and Chl as the basis for lipid-saponin carriers of subunit protein antigens

The ability of holothurian triterpene glycosides (cucumarioside A₂-2 from Cucumaria japonica, cucumarioside G₁ from C. fraudatrix, frondoside A from C. frondosa, and holotoxin A₁ from Apostichopus japonicus) to form supramolecular lipid-saponin complexes was studied. TEM demonstrated that all the studied compounds form supramolecular cholesterol-saponin complexes (nanoparticles) in aqueous medium. The complexes formed by cucumarioside A₂-2, holotoxin A₁, and frondoside A had a tubular structure and fundamentally differed in the structure from the particles produced by cucumarioside G₁. The morphology of the nanoparticles formed by cucumarioside A₂-2, holotoxin A₁, and cucumarioside G₁ changed depending on the fraction of cholesterol in the lipid-saponin system; however, this pattern was not observed for frondoside A. At the same molar fraction of cholesterol in the lipid-saponin system, cucumarioside A₂-2 formed the particles with the most pronounced tubular structure; the cholesterol-saponin complexes of holotoxin A₁ had a less pronounced tubular structure, whereas the structure of frondoside A particles was extremely heterogeneous. Comparative analysis of the morphology of the described supramolecular complexes and specific structural features of the glycosides demonstrated that the structure of the corresponding nanoparticles depended on the degree of branching of the carbohydrate moiety in the glycoside molecule and the complexation with cholesterol was determined by the specific features of aglycone structure. Thus, the feasibility of producing new generation antigen carriers using the complexes in question was proved.