Is the 135S poliovirus particle an intermediate during cell entry?

Area of Science:

• Virology
• Cell Biology
• Immunology

Background:

• Poliovirus binding to poliovirus receptor (PVR) triggers a conformational change, forming a 135S particle from the 160S native virion.
• The 135S particle is hypothesized as a cell entry intermediate, but its low infectivity and transient presence during cold-adapted mutant infections raise questions.

Purpose of the Study:

• To investigate the role and efficiency of the 135S poliovirus particle during cell entry.
• To elucidate the rate-limiting steps and PVR-independent events in poliovirus cell entry.

Main Methods:

• Studied the infectivity of 135S-antibody complexes bound to Fc receptor (CDw32).
• Analyzed poliovirus entry kinetics at 37°C and 26°C, focusing on PVR-mediated conversion and RNA release.
• Compared wild-type and cold-adapted poliovirus infection dynamics.

Main Results:

• Binding of 135S particles to Fc receptors significantly enhanced infectivity, indicating low intrinsic binding affinity.
• An additional, PVR-independent RNA release step was identified after 135S particle formation, becoming rate-limiting at 37°C.
• At 26°C, PVR-mediated conversion to 135S particles was rate-limiting, with subsequent steps occurring rapidly.

Conclusions:

• The 135S particle is a crucial intermediate in poliovirus entry, with its low efficiency partly explained by weak binding.
• Poliovirus cell entry involves a distinct, PVR-independent RNA release stage following 135S particle formation.
• Temperature influences the rate-limiting step in poliovirus entry, affecting 135S particle accumulation and subsequent events.