Studies on spin labeled ribonucleic acids encapsulated by viral proteins

Area of Science:

• Biophysics
• Structural Biology
• Virology

Background:

• Plant viruses like Tobacco Mosaic Virus (TMV) and Cowpea Mosaic Virus (CCMV) possess distinct morphologies (rod-shaped and icosahedral, respectively).
• Encapsulation of nucleic acids within viral protein shells is a fundamental biological process.

Purpose of the Study:

• To investigate the structural and dynamic properties of spin-labeled polyriboadenylic acid (sl-poly rA) encapsulated within TMV and CCMV coat proteins.
• To correlate the motion of the encapsulated sl-poly rA with the morphology of the viral coat proteins.

Main Methods:

• Electron microscopy to visualize the morphology of the resulting nucleoprotein complexes.
• Electron paramagnetic resonance (EPR) spectroscopy to study the motion and dynamics of the spin label within the encapsulated sl-poly rA.
• Enzymatic degradation assays using nucleases (exogenous nuclease and T2 ribonuclease) to assess the integrity of the nucleoprotein complexes.

Main Results:

• Nucleoprotein complexes formed were morphologically similar to the parent viruses (TMV and CCMV).
• Encapsulation led to progressive immobilization of the spin label, indicating restricted motion.
• TMV-sl-poly rA exhibited anisotropic motion, while CCMV-sl-poly rA showed isotropic motion, correlating with particle shape.
• TMV-sl-poly rA was resistant to exogenous nuclease, whereas CCMV-sl-poly rA was partially degraded by T2 ribonuclease.

Conclusions:

• The morphology of the viral coat protein influences the motion dynamics of the encapsulated sl-poly rA.
• Experimental correlation times align with theoretical calculations, suggesting tightly packed nucleoprotein particles with limited internal motion.
• Differential nuclease susceptibility indicates variations in the accessibility and packing of the encapsulated RNA within different viral structures.