Characterization of the proteinase specified by varicella-zoster virus gene 33

This study demonstrates that varicella-zoster virus (VZV) gene 33 encodes a functional proteinase essential for viral maturation. Researchers expressed VZV genes 33 and 33.5 in insect cells using recombinant baculovirus and confirmed that gene 33 produces a proteinase capable of autoproteolytic cleavage at two sites (maturation and release sites). When gene 33.5 (encoding the assembly protein precursor) was co-expressed with the proteinase, the assembly protein was processed correctly. The proteinase was purified from E. coli using affinity chromatography and demonstrated in vitro activity against assembly protein substrates. A conserved histidine residue (His-52) was identified as critical for catalytic activity, as mutation to alanine eliminated processing. Analysis of VZV-infected human cells revealed the same protein processing pattern observed in recombinant expression systems, confirming that gene 33 encodes the authentic VZV proteinase. These findings establish that the VZV proteinase functions similarly to previously characterized herpesviruses, processing both itself and structural proteins required for capsid assembly.

Key findings

• VZV gene 33 encodes an active serine proteinase capable of autoproteolytic processing at two specific cleavage sites
• The proteinase cleaves the VZV assembly protein precursor (pAP) in trans, producing a mature assembly protein product approximately 3 kDa smaller
• Histidine residue at position 52 (His-52) is essential for catalytic activity, as demonstrated by loss of activity upon His-52 to alanine mutation
• Protein processing patterns in VZV-infected human cells are identical to those produced by recombinant expression systems, validating the biological relevance of the findings
• The purified VZV proteinase demonstrated in vitro enzymatic activity toward truncated assembly protein substrates