An insightful recollection since the distorted key theory was born about 23 years ago.

During the last three decades or so, many efforts have been made to study the protein cleavage sites by some disease-causing enzyme, such as HIV (human immunodeficiency virus) protease and SARS (severe acute respiratory syndrome) coronavirus main proteinase. It has become increasingly clear via this minireview that the motivation driving the aforementioned studies is quite wise, and that the results acquired through these studies are very rewarding, particularly for developing peptide drugs.