Applicants have used protein design to develop novel functional protein architectures, termed protein kinase-inducible domains, whose structures are dependent on phosphorylation by specific protein kinases or are dependent on dephosphorylation by specific protein phosphatases. Applicants have designed kinase-inducible domains based on a modular architecture, which allows kinase-inducible domains to be responsive to any specific serine-threonine kinases. Kinase-inducible domains can consist of canonical amino acids, allowing their use as expressible tags of protein kinase activity.