Development of new methods to introduce unnatural functional molecules into native proteins for protein engineering

Proteins are one of the most sophisticated biomolecules that play important roles in many biological processes and recently have attracted much attention as a key molecular player in new fields of nanobio-science and -technology. To use protein molecules, suitable molecular interfaces for maintaining, regulating, and/or expanding the structure and activity of natural proteins are highly desirable. In addition, development of flexible strategies and new concepts to manipulate protein structures at precise atomic levels is an important challenge from the viewpoint of organic chemistry. In this account, we highlight two unique chemistry-based strategies, developed by our group, for incorporating unnatural molecules into natural proteins, which include (i) reconstitution of chemically modified cofactors with apo-proteins or -enzymes, and (ii) post-(photo) affinity labeling modification of natural proteins. Using these methods, various unnatural molecules were incorporated into natural proteins without any genetic manipulation to produce semi-artificial proteins, of which the function can be regulated, modulated, and/or read-out with help of the incorporated unnatural functionalities.