Possible Occurrence of Scale-Free Topology in Highly Statistically Associated Polymorphic Positions in Two Potyviral Proteins

We examined the associations between polymorphic positions of two potyviral proteins, HCPro and NIb, using a combined statistical and bioinformatic methodology. We constructed the relevant graph for each protein by assigning the polymorphic positions as vertices and the identified associations between them as links. We found that the relationships among positions in both molecules displayed a complex topology. In addition, the degree distribution of each network adequately fit a power law distribution, with a small number of vertices dominating a large number of associations. The graphs for both proteins shared similar topological features despite differences in protein size, similarity, functionality, and location of the coding regions in the potyviral genome. Our findings suggest that the intramolecular associations of potyviral proteins display scale free architecture, implying that this system may undergo developmental processes similar to those described for other scale free systems.