Microtubules accelerate Aurora-B activation by a reduction in dimensionality.

<p>(<b>A</b>) Schematic of a model for Aurora-B auto-activation. An active kinase (, bright red) binds to an inactive kinase (, dim red) with an equilibrium constant, , to form a complex, . The kinase reaction occurs with a catalytic constant, , producing two active kinases (<i>right</i>). (<b>B</b>) Images of P radiograms showing radioactive bands corresponding to phosphorylated INBox motif. The images correspond to 4 microtubule concentrations (labeled at <i>left</i>). The lanes in the radiogram correspond to different time points (labeled at <i>bottom</i>). At higher microtubule concentrations, the radioactive bands become more intense at earlier time points. (<b>C</b>) Plot of the INBox motif band intensity against time for 4 microtubule concentrations. (<b>D</b>) Plot of the mean first passage time, , against the size of the confining space in which the molecules diffuse, . The plot shows both 3D diffusion (red hashed line) and 1D diffusion (green solid line) using the diffusion coefficients for Aurora-B (3D case, estimated; 1D case, measured). 1D diffusion is significantly faster when the molecules diffuse within spaces 2 µm in radius.