Assembly of a spherical plant virus

Area of Science:

• Virology
• Biochemistry
• Structural Biology

Background:

• Previous in vitro virus reassembly methods used unphysiological conditions.
• In vivo viral assembly mechanisms remain incompletely understood.

Purpose of the Study:

• To establish mild, physiological conditions for cowpea chlorotic mottle virus (CCMV) in vitro reassembly.
• To characterize the properties of CCMV reassembled in vitro.
• To identify the protein subunit's active form in viral assembly.

Main Methods:

• In vitro reassembly of CCMV from isolated RNA and protein components.
• Characterization of reassembled virus using sedimentation analysis, buoyant density measurements, and electron microscopy.
• Analysis of protein subunit molecular masses at different pH levels.

Main Results:

• Successful CCMV reassembly achieved at neutral pH and ionic strength 0.2, yielding 70% encapsidation.
• Reassembled CCMV exhibited stability, sedimentation properties, molecular mass, buoyant density, and surface morphology identical to native CCMV.
• The reaction was independent of temperature (5-25°C) and did not require Mg2+ ions.
• Protein dimer identified as the active unit for CCMV reassembly.

Conclusions:

• Mild, physiological conditions enable efficient in vitro reassembly of CCMV.
• Reassembled CCMV is indistinguishable from the native virus, validating the in vitro system.
• The study identifies the protein dimer as the key functional unit in CCMV assembly.