Fig. 4.
Recognition of sulfotyrosines by SDF12. (A) NMR structure of SDF12 bound to p38-sY3. Individual subunits of the symmetric SDF12 dimer are shown in tan and white with symmetry-related p38-sY3 peptides in blue and orange. Chemical shift perturbations greater than 0.25 ppm (Fig. 2C) are highlighted in green on the surface of SDF12. Flexible regions of SDF12 (residues 1–8) and p38-sY3 (residues 29–38) are omitted for clarity. Sulfotyrosine side chains are shown in a ball-and-stick representation. In panels B–D, basic residues in SDF12 that pair with CXCR4 sulfotyrosines are shown in blue and SDF12 residues with NOEs to the sulfotyrosines are shown in green. (B) The sTyr7 residue of CXCR4 binds to SDF12 near Arg20 and makes NOE contacts with Val23. (C) The sTyr12 residue of CXCR4 occupies a cleft bounded by residues Lys27, Pro10, and Leu29 of SDF12. (D) The sTyr21 residue of CXCR4 pairs with Arg47 of SDF12 and makes NOE contacts with Val18 and Val49.