Figure 8

The SH3:P41 interface. The structure of the R21A Spc-SH3:P41 complex (backbone of SH3 in red, p41 colored yellow in space-filled representation) and the X-ray structure of Abl-SH3:P41 complex (only backbone of SH3 is shown, in green) has been superimposed on the backbone of WT Spc-SH3 (blue). Residue 21 in Spc-SH3 and the corresponding residue 15 in Abl-SH3 are represented by sticks. The long side chain at position 21 (Arg, blue sticks) in the WT structure crosses the binding interface of SH3 for p41 and explains the increase in binding affinity when replaced by an alanine (mutant R21A Spc-SH3, red sticks).