Protein-based nanotubes for biomedical applications

This review presents highlights of our latest results of studies directed at developing protein-based smart nanotubes for biomedical applications. These practical biocylinders were prepared using an alternate layer-by-layer (LbL) assembly of protein and oppositely charged poly(amino acid) into a nanoporous polycarbonate (PC) membrane (pore diameter, 400 nm), with subsequent dissolution of the template. The tube wall typically comprises six layers of poly-L-arginine (PLA) and human serum albumin (HSA) [(PLA/HSA)(3)]. The obtained (PLA/HSA)(3) nanotubes (NTs) can be dispersed in aqueous medium and are hydrated significantly. Several ligands for HSA, such as zinc(II) protoporphyrin IX (ZnPP), were bound to the HSA component in the cylindrical wall. Similar NTs comprising recombinant HSA mutant, which has a strong binding affinity for ZnPP, captured the ligand more tightly. The Fe3O4-coated NTs can be collected easily by exposure to a magnetic field. The hybrid NTs bearing a single avidin layer as an internal wall captured biotin-labeled nanoparticles into the central channel when their particle size is sufficiently small to enter the pores. The NTs with an antibody surface interior entrapped human hepatitis B virus with size selectivity. It is noteworthy that the infectious Dane particles were encapsulated completely into the hollows. Other HSA-based NTs having an alpha-glucosidase inner wall hydrolysed a glucopyranoside to yield alpha-D-glucose. A perspective of the practical use of the protein-based NTs is also described.