The various facets of protein promiscuity: not just broad specificity of proteins

Biologically active proteins have broad specificity in classical enzymology. Protein promiscuity goes far beyond that, as it makes many of their molecular recognitions quite nonspecific. Enzyme promiscuity is exemplified by catalytic promiscuity, condition promiscuity, and substrate ambiguity. It is typically mediated by protein plasticity. On the other hand, promiscuity in protein–protein interactions shown by a very large number of regulatory proteins relies mostly on intrinsic disorder in at least one of the partners.