Cardiovirus 2A as an RNA-binding protein and frameshift stimulator
(A) X-ray crystal structures of the 2A protein from EMCV (left) and TMEV (right). A zoomed-in view of the conserved ‘arginine loop’ is shown. (B) Cryo-EM structure of EMCV 2A bound to the E. coli small ribosome subunit. The arginine loop is inserted into a helical junction in the 16S rRNA. The interaction involves multiple electrostatic contacts with the ribose phosphate backbone and hydrophobic stacking of the guanidinium groups against each other and an exposed base. (C) The EMCV RNA stimulatory element is predicted to adopt both stem-loop (left) and pseudoknot (right) conformations. Conserved sequence elements important for the interaction are highlighted (yellow, left). Recognition of this element by 2A requires both the main stem (blue, right) and additional base-pairing interactions between conserved elements (red, right).