Ornithine decarboxylase encoded by chlorella virus PBCV-1

Area of Science:

• Virology
• Biochemistry
• Molecular Biology

Background:

• Chlorella virus PBCV-1 possesses a 330-kb genome.
• Ornithine decarboxylase (ODC) is a key enzyme in polyamine biosynthesis.
• Eukaryotic ODCs are well-characterized, but viral ODCs are largely unknown.

Purpose of the Study:

• To identify and characterize a potential ODC encoded by chlorella virus PBCV-1.
• To investigate the enzymatic activity and properties of the viral ODC.
• To determine the significance of this viral ODC in the context of virus infection.

Main Methods:

• Sequence analysis of the PBCV-1 genome to identify the A207R open reading frame.
• Cloning and expression of the A207R gene in Escherichia coli to produce a recombinant His-A207R fusion protein.
• Enzymatic assays to determine substrate specificity, kinetics, and optimal conditions for the recombinant protein.

Main Results:

• The A207R gene encodes a protein with 37-41% amino acid identity to eukaryotic ODCs.
• The recombinant PBCV-1 ODC catalyzes the decarboxylation of ornithine to putrescine, requiring pyridoxal 5'-phosphate.
• The enzyme exhibits optimal activity at pH 9.0 and 42°C, with a K(m) for ornithine of 0.78 mM.
• PBCV-1 ODC is sensitive to L-arginine and difluoromethylarginine but less so to difluoromethylornithine.
• The 42-kDa PBCV-1 ODC is the smallest ODC reported and is conserved among chlorella viruses.

Conclusions:

• Chlorella virus PBCV-1 encodes the first identified virus-encoded ornithine decarboxylase.
• This viral ODC is enzymatically active and plays a role in polyamine biosynthesis during PBCV-1 infection.
• The conservation of the a207r gene suggests its importance in the viral life cycle.