Evidence that polyoma polypeptide VP1 is a serine protease

Area of Science:

• Virology
• Molecular Biology
• Biochemistry

Background:

• Polyoma virus (Py) virions are composed of structural proteins, including VP1.
• Understanding virion protein processing is crucial for viral replication studies.

Purpose of the Study:

• To investigate the mechanism of polyoma virion polypeptide processing.
• To identify the enzyme responsible for proteolysis of VP1.

Main Methods:

• Dissociation of purified Py virions under specific buffer conditions (150 mM NaCl, 50 mM Tris-HCl pH 8.5, 1 mM EGTA, 3 mM DTT).
• Inhibition studies using serine protease inhibitors diisopropyl fluorophosphonate (DFP) and phenylmethyl sulfonyl fluoride (PMSF).
• Radiolabeling experiments with DFP to identify the protease activity site.

Main Results:

• Incubation of Py virions resulted in the production of two new polypeptides (43.5K and 40K) from VP1 proteolysis.
• Proteolysis was blocked by DFP and PMSF, suggesting a serine protease involvement.
• Radiolabeled DFP preferentially labeled VP1, indicating protease activity resides within VP1.

Conclusions:

• The virion-associated protease activity is a property of polyoma virus VP1.
• The 43.5K and 40K polypeptides are generated through VP1 autodigestion.
• Polyoma virus VP1 possesses intrinsic serine protease activity responsible for its own processing.