Biological system and assay for identifying modulators of tubulin ligases

1. A genetically engineered Tetrahymena cell comprising a deletion of at least two paralogs of TTLL6 or TTLL3; wherein said cell expresses tubulin exhibiting reduced polymodification compared to a wild-type Tetrahymena cell.

2. The Tetrahymena cell of claim 1 wherein the tubulin comprises shortened glutamyl side chains compared to wild-type Tetrahymena tubulin.

3. The Tetrahymena cell of claim 2 wherein at least a portion of the shortened glutamyl side chains contain less than 6 glutamic acid residues, and wherein the density of the glutamyl side chains containing less than 6 glutamic acid residues is increased relative to wild-type Tetrahymena tubulin.

4. The Tetrahymena cell of claim 2 wherein at least a portion of the shortened glutamyl side chains contain only one glutamic acid residue, and wherein the density of the glutamyl side chains containing only one glutamic acid residue is increased relative to wild-type Tetrahymena tubulin.

5. The Tetrahymena cell of claim 1 wherein the tubulin lacks glycyl side chains that are present in wild-type tubulin.

6. The Tetrahymena cell of claim 5 wherein the tubulin glycylation level is less than 90% of the tubulin glycylation level in wild-type Tetrahymena tubulin.

7. The Tetrahymena cell of claim 1 which is a TTLL6A/TTLL6F knockout cell.

8. The Tetrahymena cell of claim 1 wherein the two paralogs are selected from the group consisting of TTLL6A, TTLL6B, TTLL6C, TTLL6D, TTLL6E, and TTLL6F.

9. The Tetrahymena cell of claim 1 wherein the two paralogs are selected from the group consisting of TTLL3A, TTLL3B, TTLL3C, TTLL3D, TTLL3E, and TTLL3F.

10. The Tetrahymena cell of claim 1 which is selected from the group consisting of a TTLL6A/TTLL6F knockout cell, a TTLL6A/TTLL6B/TTLL6D/TTLL6F knockout cell, and a TTLL6A/TTLL6B/TTLL6D/TTLL6E/TTLL6F knock out cell.

11. The Tetrahymena cell of claim 1 which is selected from the group consisting of a TTLL3A/TTLL3B knockout cell, a TTLL3A/TTLL3B/TTLL3C/TTLL3D knockout cell, and a TTLL3A/TTLL3B/TTLL3C/TTLL3D/TTLL3E/TTLL3F knockout cell.

12. A method for identifying an inhibitor of a glutamic acid ligase, the method comprising:

contacting a cellular component isolated from the Tetrahymena cell of claim 1 with a candidate inhibitor compound and a glutamic acid ligase; and

detecting a change in glutamylation of the cellular component, wherein the absence of additional glutamylation is indicative of a compound that inhibits glutamic acid ligase.

13. The method of claim 12 wherein the cellular component is selected from the group consisting of an axoneme, a microtubule, a stabilized microtubule and a tubulin.

14. A method for identifying an inhibitor of a glycine ligase, the method comprising:

contacting a cellular component isolated from the Tetrahymena cell of claim 1 with a candidate inhibitor compound and a glycine ligase; and

detecting a change in glycylation of the cellular component, wherein the absence of additional glycylation is indicative of a compound that inhibits glycine ligase.

15. The method of claim 14 wherein the cellular component is selected from the group consisting of an axoneme, a microtubule, a stabilized microtubule and a tubulin.

16. A genetically engineered Tetrahymena cell comprising a disruption of at least two paralogs of TTLL6 or TTLL3; wherein the disruption is the result of homologous recombination, and wherein said cell expresses tubulin exhibiting reduced polymodification compared to a wild-type Tetrahymena cell.