Crystal structure of the N-terminal SH3 domain of mouse betaPIX, p21-activated kinase-interacting exchange factor

The mouse betaPIX-SH3 domain, residues 8-63 of P21-activated kinase interacting exchange factor, has been characterized by X-ray diffraction. Crystals belonging to space group P3(2)21 diffracted to 2.0 A and the structure was phased by the single-wavelength anomalous diffraction method. The domain is a compact beta-barrel with an overall conformation similar to the general SH3 structure. The X-ray structure shows mouse betaPIX-SH3 domain binding the way in which the betaPIX characteristic amino acids do so for an unconventional ligand binding surface. This arrangement provides a rationale for the unusual ligand recognition motif exhibited by mouse betaPIX-SH3 domain. Comparison with another SH3/peptide complex shows that the recognition mode of the mouse betaPIX-SH3 domain should be very similar to the RXXK ligand binding mode. The unique large and planar hydrophobic pocket may contribute to the promiscuity of betaPIX-SH3 domain resulting in its multiple biological functions.