Active site mutants of human herpesvirus-6 proteinase.

Amino acid residues thought to comprise the catalytic triad of HHV-6 proteinase were changed by site-directed mutagenesis in the precursor form of the proteinase. By monitoring the ability of each mutant proteinase precursor to undergo autoprocessing, Ser116, His46 and His135 were identified as catalytically crucial. An attempt was made to mimic the catalytic triad arrangement of archetypal serine proteinases by replacement of the second histidine, His135, by an Asp. Instead of increasing the autoprocessing ability of the His135Asp mutant HHV-6 proteinase precursor, this mutation had a detrimental effect since the precursor persisted predominantly in its unprocessed form.