Programmable protein circuits in living cells

1. A system comprising:

a first protease;

a second protease; and

one or more target proteins each comprising:

a first degron of the target protein that destabilizes the target protein when present on the target protein by enhancing degradation of the target protein,

a cut site specific for the first protease between the degron of the target protein and a part of the target protein, wherein the target protein is configured to be stabilized by cleavage of its cut site specific for the first protease,

another degron of the target protein, and

a cut site specific for the second protease connected to the other degron of the target protein, wherein the target protein is configured to be destabilized by cleavage of the cut site specific for the second protease regardless of whether the first degron of the target protein is present on the target protein.

2. The system of claim 1 , wherein the other degron of each target protein comprises an N-end degron that is conditional on cleavage of the cut site specific for the second protease.

3. The system of claim 1 , further comprising a third protease comprising a cut site specific for the second protease, wherein the third protease is configured to be deactivated by cleavage of its cut site specific for the second protease; and wherein the second protease comprises a cut site specific for the third protease, wherein the second protease is configured to be deactivated by cleavage of its cut site specific for the third protease.

4. The system of claim 1 ,

wherein the second protease further comprises a first domain of the second protease, a second domain of the second protease, a first complementary association domain, and an optional second complementary association domain of the second protease connected to the first or second domain of the second protease;

wherein the first domain of the second protease comprises the cut site specific for the third protease;

wherein the second domain of the second protease comprises another cut site specific for the third protease;

wherein the first complementary association domain of the second protease optionally comprises two parts of the complementary association domain of the second protease, each part of the complementary association domain of the second protease connecting to one of the second protease's cut sites specific for the third protease; and

wherein the second protease is configured to be deactivated by cleavage of either of its cut sites.

5. The system of claim 1 , wherein the third protease further comprises an optional association domain of the third protease, and wherein cleavage of the third protease's cut site by the second protease removes at least part of a cleavage domain of the third protease, thereby deactivating the third protease.

6. The system of claim 1 , wherein the stability of the target proteins comprises an analog behavior that is dependent on a concentration of the first protease, wherein a higher concentration of the first protease has a greater stabilizing effect on the target proteins than a lower concentration of the first protease.

7. The system of claim 1 , wherein the stability of the target proteins comprises an analog behavior that is dependent on a concentration of the second protease, wherein a higher concentration of the second protease has a greater destabilizing effect on the target proteins than a lower concentration of the second protease.

8. The system of claim 7 , wherein the concentration of the second protease is decreased by a higher concentration of the third protease as compared to a lower concentration of the third protease or by a higher amount of a nucleic acid encoding the third protease as compared to a lower amount of a nucleic acid encoding the third protease.

9. The system of claim 7 , wherein the analog behavior of the target protein that is dependent on a concentration of the second protease is more sharp and/or comprises a greater threshold for destabilizing the target protein at a higher concentration of the third protease as compared to a lower concentration of the third protease, or at a higher amount of a nucleic acid encoding the third protease as compared to a lower amount of a nucleic acid encoding the third protease.

10. The system of claim 1 ,

wherein the first protease further comprises a first domain of the first protease and a second domain of the first protease;

wherein the first domain of the first protease connects to a first conditional dimerization domain of the first protease;

wherein the second domain of the first protease connects to a second conditional dimerization domain of the first protease;

wherein the first and second conditional dimerization domains of the first protease are configured to dimerize with each other upon binding a dimerizing agent.

11. The system of claim 10 , wherein the conditional dimerization domains of the first protease each comprise one of an FK506 binding protein (FKBP), GyrB, GAI, Snap-tag, eDHFR, BCL-xL, CalcineurinA (CNA), CyP-Fas, FRB domain of mTOR, GID1, HaloTag, and/or Fab (AZ1).

12. The system of claim 10 , wherein the dimerizing agent comprises FK1012, FK506, FKCsA, Rapamycin, Coumermycin, Gibberellin, HaXS, TMP-HTag, or ABT-737.

13. The system of claim 1 , wherein the first protease comprises tobacco etch virus protease (TEVP).

14. The system of claim 1 , wherein the second protease comprises tobacco vein mottling virus protease (TVMVP).

15. The system of claim 1 , wherein one target protein of the one or more target proteins comprises Citrine.

16. The system of claim 1 , wherein one target protein of the one or more target proteins comprises, from the N-terminal to the C-terminal of the one target protein, an N-end degron as the other degron comprising a tobacco vein mottling virus protease (TVMVP) cut site specific for the second protease, Citrine, a tobacco etch virus protease (TEVP) cut site as the cut site specific for the first protease, and a non-N-end degron as the first degron.