Fig. 4. (A) Structure of the central region of a representative conformer of the CRIB motif of WASP with Cdc42 (PDB ID code 1cee). The coloring scheme is as shown in Figure 3. (B) For comparison, the sequence-specific interactions of the semi-CRIB motif of Par6 are shown in a similar orientation as in (A). (C) Asp38 is not required for binding of Par6 to Cdc42. Myc-tagged Par6B or, as a control, the CRIB domain of α-PAK, was immunoprecipitated from cells co-expressing GST fusions of Cdc42(Val12) that contain second mutations in the Switch I region. Bound GST–Cdc42 was detected by blotting with anti-GST antibody.