Many of the drugs that we use today work by suppressing, enhancing, and regulating the functions of specific proteins. The interactions between drug molecules and their target proteins follow what can be understood as a “lock and key” relationship, so the mechanisms greatly depend on the individual structures. While many different proteins are known to exist in nature, it is believed that they share a relatively small number of basic structures. It is estimated that one-third of these structures have been identified so far. Identifying more of these basic protein structures will facilitate the prediction of the structures of the target proteins of drug molecules, and consequently will provide valuable basic information for drug design.