VPg Impact on Ryegrass Mottle Virus Serine like 3C Protease Proteolysis and Structure

Sobemoviruses encode serine like 3C proteases Pro that participate in the processing and maturation of other virus encoded proteins. Its cis and trans activity is mediated by the naturally unfolded virus genome linked protein VPg . Nuclear magnetic resonance studies show a Pro VPg complex interaction and VPg tertiary structure; however, information regarding structural changes of the Pro VPg complex during interaction is lacking. Here, we solved a full Pro VPg 3D structure of ryegrass mottle virus RGMoV that demonstrates the structural changes in three different conformations due to VPg interaction with Pro. We identified a unique site of VPg interaction with Pro that was not observed in other sobemoviruses, and observed different conformations of the Pro amp; 946;2 barrel. This is the first report of a full plant Pro crystal structure with its VPg cofactor. We also confirmed the existence of an unusual previously unmapped cleavage site for sobemovirus Pro in the transmembrane domain E A. We demonstrated that RGMoV Pro in cis activity is not regulated by VPg and that in trans, VPg can also mediate Pro in free form. Additionally, we observed Ca2 and Zn2 inhibitory effects on the Pro cleavage activit