Protein-based self-assembly bridging system with cassette tags

The affinity of gold particles to thiolated DNA strands with complementary sequences has been utilized extensively for self-assembly systems in the scale ranging from micrometers to nanometers. This paper represents a new approach based on the method of protein-based self-assembly system using the property which has been employed in protein purifications for years that Ni-NTA (nickel-nitrilotriacetic acid) resin shows remarkable selectivity to proteins containing an affinity tag of amino acid residues cassette composed of six consecutive histidine residues, i.e., 6xHis tag. The designs and utilities of protein-based self-assembly system can be carried out with: (1) antibody/antigen-based self-assembly, (2) receptor/ligand-based self-assembly, (3) oligopeptide/oligopeptide-based self-assembly, and (4) DNA/DNA-binding protein-based self-assembly, etc. The modification of proteins with 6xHis tags, for being immobilized on the Ni-NTA pre-coated inorganic materials, can be prepared using commercialized protein expression systems or developed peptide synthetic techniques. The modified proteins would be linked onto the treated particles dictated by the affinity between Ni-NTA and 6xHis moiety. Then, mixing the two different proteins linked particles would cause the self-assembly between two particles via the interactions of utilized protein-based self-assembly systems. In addition to the demonstrated model using the affinity of 6xHis tags to chelated nickel ions proposed in this study, protein with exposed imidazole rings of histidines also have affinity for certain transition metal ions, such as Mn²⁺, Fe³⁺, Co²⁺, Cu²⁺, and Zn²⁺, etc., for linking up the proteins or oligopeptides to inorganic materials. Due to the development of genetic engineering and solid phase peptide synthesis technologies, the ease of producing recombinant proteins or synthetic oligopeptides makes the choice of protein-based self-assembly materials more versatile and convenient than its counterparts. The protein-based self-assembly systems with cassette tags can be options in addition to the well known DNA-based self-assembly method, i.e., the affinity of gold particles to thiolated DNA strands with complementary sequences, thus broaden up the scope for "bottom-up- " fabrication approaches in nanotechnology.