Structural basis of protein-protein interactions.

Regulated interactions between proteins govern signaling pathways within and between cells. Although it is possible to derive some general principles of protein-protein recognition from experimentally determined structures, recent structural studies on protein complexes formed during signal transduction illustrate the remarkable diversity of interactions, both in terms of interfacial size and nature. There are two broad classes of complexes: "domain-domain," in which both components comprise prefolded structural units, and "domain-peptide," in which one component is a short motif that is unstructured in the absence of its binding partner. Signaling complexes often involve multidomain proteins whose multifaceted binding functions are regulated by intramolecular domain interactions. The structural basis of regulation, via steric and allosteric mechanisms, is discussed.