IFIT3 and IFIT2/3 promote IFIT1-mediated translation inhibition by enhancing binding to non-self RNA

Renata C Fleith; Harriet V Mears; Edward Emmott; Stephen C Graham; Daniel S Mansur; Trevor R Sweeney

Despite considerable evidence for IFIT oligomerisation, little is known about how different IFITs interact and what impact this interaction has on function. To address this, here we have reconstituted different IFIT complexes from individually purified proteins, determined the oligomeric state of each and reveal for the first time that interaction with IFIT3 or a heterocomplex of IFIT2 and IFIT3 enhances the cap0 RNA binding and translation inhibition activity of IFIT1. We also demonstrate in vitro that although IFIT2 and IFIT3 individually form stable homodimers, the IFIT2:IFIT3 dimer complex is the energetically more stable species. Our results provide a critical missing link between IFIT oligomerisation and function, and present a mechanistic framework for understanding the role of IFITs in the host immune response.