Putative papain-related thiol proteases of positive-strand RNA viruses Identification of rubi- and aphthovirus proteases and delineation of a novel conserved domain associated with proteases of rubi-, α- and coronaviruses

Gorbalenya, Alexander E.; Koonin, Eugene V.; Lai, Michael M.-C.

Abstract A computer-assisted comparative analysis of the amino acid sequences of (putative) thiol proteases encoded by the genomes of several diverse groups or positive-stranded RNA viruses and distantly related to the family of cellular papain-like proteases is presented. A high level of similarity was detected between the leader protease of foot-and-mouth-disease virus and the protease of murine hepatitis coronavirus which cleaves the N-terminal p28 protein from the polyprotein. Statistically significant alignment of a portion of the rubella virus polyprotein with cellular papain-like proteases was obtained, leading to tentative identification of the papain-like protease as the enzyme mediating processing of the non-structural proteins of this virus. Specific grouping between the sequences of the proteases of α-viruses, and poty- and bymoviruses was revealed. It was noted that papain-like proteases of positive-stranded RNA viruses are much more variable both in their sequences and in genomic locations than chymotrypsin-related proteases found in the same virus class. A novel conserved domain of unknown function has also been identified which flanks the papain-like proteases of α-, rubi- and coronaviruses.