The ability of eukaryotic cells to adopt variable shapes, to move in different directions, or to distribute cell components within the cytoplasm is controlled by a network of filaments: the cytoskeleton. Microtubules are the major type of cytoskeletal filaments, consisting of linear polymers of tubulin proteins. Microtubules provide intracellular tracks for organellar transport performed by molecular motors (such as kinesins and dyneins). One unaswered question is how motor proteins are targeted to specific microtubules.

We hypothesize that distinct types of microtubules are adapted for specific functions by post-translational modifications (acetylation, detyrosination, polyglycylation and polyglutamylation) which affect the c-terminal tail domains of alpha- and beta-tubulin. We are studying a unicellular organism, the ciliate Tetrahymena thermophila, which assembles at least 18 distinct microtubular structures in a single cell. Subsets of microtubular organelles in Tetrahymena have a unique combination of post-translational modifications. For example, polyglutamylation is highly concentrated in the basal bodies while polyglycylation affects mainly cilia and cortical microtubules. We showed that specific amino acid residues involved in either polyglycylation or polyglutamylation are required for assembly of the ciliary 9+2 axoneme and proper severing of cortical microtubules (Thazhath et al., NCB, 2002; Thazhath et al. Mol. Biol. Cell 2004). In collaboration with Drs. Carsten Janke and Bernard Edde, we have recently identified the enzymes resposible for tubulin polyglutamylation (Janke et al., Science 2005).

Current research projects include studies on:

1) Proteins which are regulated by tubulin modifications (motors and structural MAPs)

2) Purification and identification of tubulin glycylases.

3) Role of tubulin glutamylase enzymes in vivo.

4) Structural aspects of tubulin glutamylases.

5) Transport and folding of tubulins inside complex organelles such as cilia.

6) Studies on the role of microtubule-associated kinases (NIMA type) in assembly of microtubular organelles and size regulation of organelles.

7) Tetrahymena as a vehicle for expression of foreign proteins of biotechnological importance.