Fig. 1: A schematic diagram for EV71 RdRP EC assembly, crystallization, and crystal soaking and a six-state model for the viral RdRP NAC.

a The EC was assembled using the T35/P10 construct upon addition of a G-A-G-A-G-A hexa-nucleotide. The 16-mer (P16)-containing EC was crystallized and subjected to different soaking trials to capture various NAC states. b The previously proposed six-state RdRP NAC starts with the state 1 (S1) complex with an empty and open conformation active site, and the NTP binding leads to the state 2 (S2) complex that remains in the open conformation. In most cases, the cognate NTP induces a conformational change to close the active site (corresponding to the active site closure) to reach state 3 (S3), and then completion of the phosphoryl transfer indicates the formation of the state 4 (S4) complex that remains in the closed conformation. The active site often resets to open conformation before translocation and the corresponding complex was assigned as the state 5 (S5) complex. The state 6 (S6) complex represents any intermediates that poised between the pre- and post-translocation states. The representative PDB entries are provided next to the state symbols and reference entries used to help present the intermediate structures in this study are shown in blue.