The modular logic of signaling proteins: building allosteric switches from simple binding domains.

Many eukaryotic signal transduction proteins have component-based architectures: they are built from combinations of protein interaction domains and catalytic domains. Intact, these proteins display the sophisticated allosteric behavior required for cellular regulation; the protein's output activity is tightly repressed under basal conditions, but can be robustly activated by a specific set of input effector ligands. A combination of structural, biophysical and computational studies is beginning to shed light on the fundamental principles governing this type of modular allostery.