Table 3.

Toolkit of Modulators

Modulator	Implementation	Utility
Alanine mutation	Mutate sector-connected surface residues to alanine	Scan for functional sites
Saturation mutagenesis	Mutate sector-connected surface residues to all amino acids	Screen for gain-of-function and neomorphic activity
Light-activated domain (e.g. LOV, CRY or Phy domains)	Introduce LOV or other domains that undergo conformational changes upon exposure to specific wavelengths of light at sector-connected surface residues	Conditional regulation by an orthogonal signal
Hormone-binding domain (e.g. estradiol, progesterone or glucocorticoid binding domains)	Introduce ligand binding domains from nuclear hormone receptors that change conformation upon binding to cognate hormones at sector-connected surface residues; can restrict localization of target protein to the cytoplasm	Conditional regulation by an orthogonal signal
Periplasmic solute-binding protein domains	Introduce maltose binding protein domain	Conditional regulation by an orthogonal signal
Nucleic acids	Introduce nucleic acid binding domain	Nucleic acid libraries can be synthesized
Phosphorylation sites	Introduce consensus motifs from kinases of interest at sector-connected surface residues	Conditional regulation by orthogonal or endogenous signaling pathways
Protein-protein interaction domain	Introduce protein-protein interaction domain for a protein of interest at sector-connected surface residues	Conditional regulation by interaction with signaling proteins; can be used as second wave signaling in complex circuits