Entropy-driven polymerization of ribgrass virus protein

Area of Science:

• Virology
• Protein Biochemistry
• Biophysical Chemistry

Background:

• Holmes ribgrass virus (HRV) is serologically related to tobacco mosaic virus (TMV).
• HRV protein has a distinct amino acid composition compared to TMV protein, notably containing histidine and methionine residues absent in TMV.
• Understanding HRV protein's polymerization is key to its classification and function.

Purpose of the Study:

• To investigate the biophysical properties of Holmes ribgrass virus (HRV) protein polymerization.
• To compare the polymerization characteristics of HRV protein with those of tobacco mosaic virus (TMV) and E66 proteins.
• To elucidate the structural and thermodynamic differences between HRV and TMV proteins.

Main Methods:

• Ultracentrifugation was used to determine sedimentation properties of HRV protein.
• Hydrogen ion titration was employed to analyze proton binding during polymerization.
• Thermodynamic parameters, including enthalpy of polymerization, were calculated.

Main Results:

• HRV protein polymerization is entropy-driven, forming a 20S component, similar to TMV.
• Unpolymerized HRV protein sediments at 3S (dimer) versus 4S for TMV.
• HRV protein shows lower enthalpy of polymerization (18,400 cal/mol) and different H+ ion binding stoichiometry (1 mol/mol) compared to TMV.
• Significant hydrogen ion binding by unpolymerized HRV protein was observed, unlike TMV and E66 proteins.

Conclusions:

• HRV protein polymerization shares some similarities with TMV, particularly the entropy-driven nature and formation of a 20S species.
• Significant differences in sedimentation, thermodynamic properties, and hydrogen ion binding distinguish HRV protein from TMV and E66 proteins.
• These findings highlight unique biophysical characteristics of HRV protein, suggesting distinct structural and functional properties despite serological relation to TMV.