[Applications of the motif-programmed proteins in medical area]

Motif-programming is a method for creating artificial proteins by combining functional peptide motifs in a combinatorial manner. Motifs are often short amino acid sequences within natural proteins that are associated with particular biological functions. Motifs also can be created de novo using molecular engineering. In particular, peptide aptamers, which have been isolated as specific binders against various targets, are believed to be promising motif blocks for creating novel biomaterials through motif-programming. It is now known, however, that simple arithmetic addition does not always work with motif-programming-e.g., simple conjugation of motifs-A and -B does not always result in a bifunctional peptide-AB. To solve this nonlinearity in motif-programming, we have been employing a combinatorial approach, which we called MolCraft. In MolCraft, we prepare a library of artificial proteins that contain multiple motifs in various numbers and orders, from which clones having the desired functions are selected. In MolCraft, a microgene is first rationally designed so that the encoded peptides contain motifs, and then tandemly polymerized with insertion or deletion mutations at the junctions between microgene units. Because of junctional perturbations, proteins translated from a single microgene polymer are molecularly diverse, originating from the combinatorics of three reading frames, and are thus combinatorial polymers of three peptides. By embedding functional motifs into different reading frames of a single microgene, combinatorial polymers of functional motifs are easily prepared. Notably, repetitiousness retained in the overall structure of proteins contributes to the formation of ordered structures, and enhances the chances of reconstituting biological activity. This method is particularly well suited for developing liaison molecules that interface between cells and inorganic materials. Examples of multifunctional artificial proteins created from this method will be introduced.