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 coronavirus, mouse hepatitis virus strain A59 (MHV), expresses a chymotrypsin-like cysteine proteinase (3CLpro) within the gene 1 polyprotein. The MHV 3CLpro is similar to the picornavirus 3C proteinases in the relative location of confirmed catalytic histidine and cysteine residues and in the predicted use of Q/(S, A, G) dipeptide cleavage sites. However, less is known concerning the participation of aspartic acid or glutamic acid residues in catalysis by the coronavirus 3Clike proteinases or of the precise coding sequence of 3CLpro within the gene 1 polyprotein. In this study, aspartic acid residues in MHV 3CLpro were mutated and the mutant proteinases were tested for activity in an in vitro trans cleavage assay. MHV 3CLpro was not inactivated by substitutions at Asp 3386 (D53) or Asp 3398 (D65), demonstrating that they were not catalytic residues. MHV 3CLpro was able to cleave at a glutamine-glycine (QG 3607-8 ) dipeptide within the 3CLpro domain upstream from the predicted carboxy-terminal QS 3635-6 cleavage site of 3CLpro. The predicted full-length 3CLpro (S 3334 to Q 3635 ) had an apparent mass of 27 kDa, identical to the p27 3CLpro in cells, whereas the truncated proteinase (S 3334 to Q 3607 ) had an apparent mass of 24 kDa. This 28-amino-acid carboxy-terminal truncation of 3CLpro rendered it inactive in a trans cleavage assay. Thus, MHV 3CLpro was able to cleave at a site within the putative full-length proteinase, but the entire predicted 3CLpro domain was required for activity. These studies suggest that the coronavirus 3CL-proteinases may have a substantially different structure and catalytic mechanism than other 3C-like proteinases. ᭧ 1997 Academic Press

Determinants of Mouse Hepatitis Virus 3C-like Proteinase Activity