Spatial organization of signaling cascades.

<p>(<b>A</b>) Sketch of the classical temporal signal transduction model. Extension of this model into three-dimensional space naturally results in a variety of different spatial motifs. (<b>B</b>) The signal is first processed by signaling components tethered to the membrane, and then transduced at membrane-cytosolic interface into the cytosol. (<b>C</b>) The signaling components are directly activated at the membrane-cytosolic interface and diffuse through the cytosol. Note that diffusion coefficients for lateral diffusion along the membrane are much lower than in the cytosol.