Construction of an energy transfer system in the bio-nanocup space by heteromeric assembly of gp27 and gp5 proteins isolated from bacteriophage T4

Protein assemblies, such as viruses and ferritins, have been employed as useful molecular templates for the accumulation of organic and inorganic compounds to construct bio-nanomaterials. While several methods for conjugation of heterofunctional molecules with protein assemblies have been reported, it remains difficult to control their fixation sites in the assemblies. In this article, we demonstrate the three-dimensional arrangement of different types of fluorescent probes using the heteromeric self-assembly of (gp27-gp5)3 which is the component protein of bacteriophage T4 (gp: gene product). The composites exhibited fluorescence resonance energy transfer from fluorescein to tetramethylrhodamine dyes immobilized in the bio-nanocup space. The alternation of the donor and acceptor positions induced fluorescence self-quenching by the formation of ground-state complexes of the acceptors. These results indicate that the site-specific conjugation method using the bio-nanocup space of the heteromeric protein assembly has potential for the integration of several types of functional molecules in protein nanospaces.