Fig. 5. Structure of the complex of the p67^phox SH3(C) and the p47^phox tail peptide. (A) Overlay of the 22 NMR structures. The residues used for superimposing the different structures are colored blue (SH3) and red (the tail peptide), and the other residues are in gray. Residue numbers of the p47^phox tail peptide are labeled with a prime (′). (B) Ribbon representation of the lowest energy structure. The β-strands of the p67^phox SH3(C) are colored blue: β1, residues 460–463; β2, 483–491; β3, 494–498; β4, 503–506; and the 3₁₀-helix is colored green: residues 508–510. The PxxP motif and the two α-helices of the p47^phox tail peptide are drawn in red and orange, respectively. Side chains located within the binding interface are shown in pink (SH3) and in yellow (the tail peptide). (C) The same structure viewed from a different angle. The side chains of Leu375′, Lys383′ and Leu386′, colored yellow, fill the space between the two α-helices. The positions of the three SH3 loops are shown.