Fig. 2: Structural basis of nucleotide recognition.
From: Structural basis for substrate selection by the SARS-CoV-2 replicase
a, Cryo-EM density of the 2.7 Å nominal resolution +GTP structure (S4_GTP), coloured according to the fitted model chains. b, Cryo-EM density of the bound incoming GTP, two associated metal ions and the nearby bases of the t-RNA and p-RNA strands. c, Close-up of the active site of the apo complex PDB 7RE1 (ref. 18), illustrating the arrangement of the conserved RdRp active site motifs A–D and F (crimson, hot pink, gold, salmon and magenta, respectively) and of key residues when the NTP binding site (dashed red line) is empty. d, Comparison of the S4_GTP and apo structure (faded grey) active sites, highlighting observed motif/residue rearrangements (blue arrows) on NTP binding. Movements in motifs A and D close the active site. e, Schematic depicting nucleotide addition, in the presence of an intact 3′-OH, based on disposition of magnesiums and NTP in the S4_GTP structure. f, 2D schematic of the suite of interactions involved in NTP binding based on distances in the S4_GTP structure. Residues interacting indirectly or weakly with the NTP are faded for clarity.
