Protein-based nanotechnology: molecular construction of proteins

Methods for the molecular construction of proteins were examined with photosynthetic reaction centers (RCs ) from photosynthetic bacteria. RCs were used because the proteins are resistant to denaturation. The orientation of RCs in Langmuir-Blodgett (LB) films was examined. To give the polar distribution of hydrophobicity/hydrophilicity, cytochrome c from horse heart was cross-linked chemically to an edge of the molecule of RC. The orientation of the cross-linked complex was well organized whereas that of native RC was random at the air-water interface. Highly packed RCs in the film were obtained using the interaction with quinonylphospholipid (Q-DPPE). A monolayer of Q-DPPE was formed on the water surface to which quinone-depleted bacterial photosynthetic reaction centers (RC(−Q)s) bound to form an oriented RC-LB film. The cross-linked complex oriented unidirectionally in negatively charge liposomes. A light-harvesting system for energy transfer to RC was constructed using bacteriochlorophylls or chlorophylls incorporated in liposomes together with RCs. Both pigments collected light quanta efficiently and transferred them to bacterial RCs. RCs in the chromatophore membrane were also immobilized unidirectionally using the avidin-biotin interaction.