Cleavage of poliovirus-specific polypeptide aggregates

Area of Science:

• Virology
• Molecular Biology
• Biochemistry

Background:

• Poliovirus assembly involves the synthesis and processing of viral polypeptides.
• Understanding the dynamics of viral protein aggregation and cleavage is crucial for comprehending the viral life cycle.

Purpose of the Study:

• To characterize the aggregates of poliovirus type 2 cytoplasmic polypeptides.
• To investigate the processing of the viral precursor polypeptide NCVP1a and its role in capsid formation.

Main Methods:

• Zonal electrophoresis to resolve polypeptide aggregates.
• Sodium deoxycholate (DOC) treatment and ultracentrifugation to analyze aggregate properties.
• Analysis of polypeptides synthesized in iodoacetamide-treated infected cells.
• In vitro cleavage assays using infected and uninfected cell extracts.

Main Results:

• Two distinct aggregates of poliovirus type 2 polypeptides were identified: one with noncapsid viral-specific polypeptides (NCVP) 2 and x, and another with capsid polypeptides (VP).
• The precursor polypeptide NCVP1a accumulates in the presence of iodoacetamide and migrates with the NCVP2-x aggregate.
• Infected cell extracts, but not uninfected cell extracts, cleave NCVP1a into capsid polypeptides, which then dissociate from the NCVP2-x complex.
• The capsid polypeptide aggregate can be converted to an empty capsid-like form upon heating.

Conclusions:

• Poliovirus type 2 polypeptides form distinct aggregates, with NCVP2 and NCVPx forming one and capsid proteins another.
• A protease present in infected cells is responsible for cleaving NCVP1a, initiating the formation of infectious virions.
• The cleavage of NCVP1a is a critical step in poliovirus maturation, leading to the release of capsid proteins.