Characterization of the adenovirus proteinase: development and use of a specific peptide assay.

An assay system has been developed for the adenovirus endoproteinase which utilizes the synthetic peptide MSGGAFSW, derived from the cleavage site of the adenovirus type 2 (Ad2) protein pVI. MSGGAFSW was shown to be cleaved at the G-A bond when incubated with a source of Ad2 proteinase. Digestions were readily monitored by either fast protein liquid chromatography or thin layer electrophoresis, enabling the rapid production of quantitative data. Comparison of the peptide assay with a previously described [35S]methionine assay system showed it to be faster, cleaner and less prone to extreme conditions of pH and ionic strength. The effect on adenovirus proteinase activity of a number of inhibitors was assessed using both the [35S]methionine and peptide assays. Identical inhibitor profiles were obtained and these suggested that the adenovirus enzyme is a cysteine proteinase. The 23K gene product, thought to be the proteinase, contains cysteine and histidine residues at positions 122 and 54, respectively, that could constitute part of the active site of a cysteine proteinase. These amino acids and their surrounding residues are conserved in all serotypes examined and appear to bear some resemblance to those in the putative active sites of the 3C proteinases in picornaviruses.