Figure 8.

Center-of-mass distance between the ${\mathrm{3}}_{\mathrm{10}}$ α helices of (a) p27, p27 Y2P74, p27 Y2P88, p27 Y2P88 Y2P89, p27 Y2P89 and (b) p21, p21 Y2P77, p57, p57 Y2P63, p57 Y2P91 and the active-site pocket. Some equilibrium distances appear to be above/below 10 Å because as the phosphorylation state is altered, the center of mass of that group of atoms will be shifted. Of all the various tyrosine phosphorylation states of p27, we only observe dissociation of the inhibitory ${\mathrm{3}}_{\mathrm{10}}$ α helix when Y88 has been phosphorylated. When both Y88 and Y89 are phosphorylated, the α helix fluctuates between a bound and partially unbound state, indicating that phosphorylated Y89 might aid in preventing the dissociation of the inhibitor when Y88 is phosphorylated. To see this figure in color, go online.