Functional regulation of PVBV Nuclear Inclusion protein-a protease activity upon interaction with Viral Protein genome-linked and phosphorylation.

Regulation of NIa-Pro is crucial for polyprotein processing and hence, for successful infection of potyviruses.
We have examined two novel mechanisms that could regulate NIa-Pro activity. Firstly, the influence of VPg
domain on the proteolytic activity of NIa-Pro was investigated. It was shown that the turnover number of
the protease increases when these two domains interact (cis: two-fold; trans: seven-fold) with each other.
Secondly, the protease activity of NIa-Pro could also be modulated by phosphorylation at Ser129. A mutation
of this residue either to aspartate (phosphorylation-mimic) or alanine (phosphorylation-deficient) drastically
reduces the protease activity. Based on these observations and molecular modeling studies, we propose
that interaction with VPg as well as phosphorylation of Ser129 could relay a signal through Trp143 present
at the protein surface to the active site pocket by subtle conformational changes, thus modulating protease
activity of NIa-Pro.