Fig. 4. Mechanism of axin-dependent activation of HIPK2 kinase activity.
HIPK2 is held in an inactive state by interactions between its kinase and axin-binding domains (KD and AD, respectively). Upon binding axin, inhibition is relieved and the KD is able to phosphorylate both the HIPK2-bound p53 molecule and the one bound to axin. Binding sites of HIPK2 and p53 on axin are depicted approximately to scale (see Fig. 3). Based on Fig. 8 of Rui et al. (Rui et al., 2004).