Figure 1.

Interaction of VP39 with m³Ade. (a) The 1.83-Å difference electron density of VP39 crystal soaked in 10 mM m³Ade contoured at the 2.5σ level (see Table 1 and Materials and Methods). Dashed lines represent hydrogen bonds (cyan) and salt links (magenta). (b) Equivalent to a but soaked in 10 mM adenine and with a 1.92-Å difference Fourier (Table 1). (c) Stacking of the adeninium ring of m³Ade with the aromatic side chains of Tyr 22 and Phe 180, projected parallel to the base ring. The atomic surface is shown in mesh representation. The (N)3-methyl group lies 6 Å from the peptide carbonyl oxygen of Tyr 204. (d) Same as c but projected perpendicular to the base ring with surface mesh and peptide backbone omitted for clarity.