Fig. 5.
Crystal structures of the apo and nucleotide-bound mutant PA endonuclease domains from the pH1N1 influenza virus (construct PANΔLoop). (A) apo F105S mutant. (B) apo E119D. (C) F105S in complex with dTMP/rUMP. (D) E119D in complex with dTMP/rUMP. In each figure, the protein secondary structure is shown in gray/blue, amino acids in stick representation with green carbons, water molecules as red spheres, and metal ions as teal spheres. In C and D, the two substrate-bound structures are superimposed. The amino acids with green carbons correspond to the rUMP (peach carbons) complex structure, and those with pink carbons correspond to the dTMP (also pink carbons) complex. In the F105S complexes (C), the structures are almost identical apart from the orientation of Tyr24. In the E119D complexes (D), there are substantial differences between the two structures. Hydrogen bonds and metal coordination are displayed by dashed lines. The electron densities are shown in SI Appendix, Fig. S7.