Interaction of nonstructural protein 5A of the hepatitis C virus with Src homology 3 domains using noncanonical binding sites.

Src homology 3 (SH3) domains are widely known for their ability to interact with other proteins using the canonical PxxP binding motif. Besides those well-characterized interaction modes, there is an increasing number of SH3 domain-containing complexes that lack this motif. Here we characterize the interaction of SH3 domains, in particular the Bin1-SH3 domain, with the intrinsically disordered part of nonstructural protein 5A of the hepatitis C virus using noncanonical binding sites in addition to its PxxP motif. These binding regions partially overlap with regions that have previously been identified as having an increased propensity to form α-helices. Remarkably, upon interaction with the Bin1-SH3 domain, the α-helical propensity decreases and a fuzzy complex is formed.