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 .