Definition: In this task, you're given a paragraph from the research paper and your task is to generate a suitable title for the research paper based on the given paper. Under 100 words is a good title length.
Input: The main peptidase (M pro ) from the coronavirus (CoV) causing severe acute respiratory syndrome (SARS) is one of the most attractive molecular targets for the development of anti-SARS agents. We report the irreversible inhibition of SARS-CoV M pro by an aza-peptide epoxide (APE; k inact /K i Z 1900(G400) M K1 s K1 ). The crystal structures of the M pro :APE complex in the space groups C2 and P2 1 2 1 2 1 revealed the formation of a covalent bond between the catalytic Cys145 S g atom of the peptidase and the epoxide C3 atom of the inhibitor, substantiating the mode of action of this class of cysteine-peptidase inhibitors. The aza-peptide component of APE binds in the substrate-binding regions of M pro in a substrate-like manner, with excellent structural and chemical complementarity. In addition, the crystal structure of unbound M pro in the space group C2 revealed that the "N-fingers" (N-terminal residues 1 to 7) of both protomers of M pro are well defined and the substrate-binding regions of both protomers are in the catalytically competent conformation at the crystallization pH of 6.5, contrary to the previously determined crystal structures of unbound M pro in the space group P2 1 .

Crystal Structures of the Main Peptidase from the SARS Coronavirus Inhibited by a Substrate-like Aza-peptide Epoxide