RDV virion entry into Nasuia periplasmic space was mediated by specific interaction between RDV P8 and Nasuia porin. (a) Secondary structure prediction showed that Nasuia porin consisted of 18 β-strands and six transmembrane regions. (b) RDV virion consists of one minor outer capsid protein P2 and one major outer protein P8. Scale bar; 50 nm. (c) Yeast two-hybrid assay to detect interactions between P2N (15 nm domain, 1–688 aa) or RDV P8 and Sulcia OMP (BSA domain, 706–985 aa) or Nasuia porin. (d) GST pull-down assay to detect interactions between RDV P8 and Nasuia porin. Nasuia porin-GST acted as a bait protein with GST as a control. Pull-down samples were probed with GST antibody in a western blot. (e) Proposed model for the different binding strategies for RDV virions with the envelopes of Sulcia and Nasuia. IM, inner membranes; OM, outer membranes; OMP, outer membrane protein; PS, periplasmic space.