The polyglutamylase enzyme family: which enzyme is doing what? – Pgases

Polyglutamylation is an original posttranslational modification of proteins. The modified proteins receive a side chain of glutamate residues that is of variable length. Although known since the early nineties, this modification has not been functionally explored because the modifying enzymes have remained obscure. The first polyglutamylases (TTLL1) has now been discovered in our lab and we have realised that more enzymes exist. Knowing the potential importance of polyglutamylation for neuronal differentiation, cell cycle control, centrosome integrity and axoneme function, we now want to initiate functional studies on polyglutamylases. We will investigate the influence of polyglutamylation on diverse biological processes by using different experimental models: cell culture, cell free extracts and whole organisms (C. elegans, knock-out mice). From the present perspective, polyglutamylation is mostly involved in microtubule function. The fact that several microtubule-associated proteins are sensitive to the degree of microtubule polyglutamylation suggests that the differential modification of the tubules regulates all kinds of microtubule-mediated events, and also the stability of the cytoskeleton itself. We hope this will advance the understanding of the versatile role of microtubules and of how these structures adapt to and regulate so many different cellular processes. In our lab, we have started to identify new polyglutamylase enzymes and to produce tools to work on these proteins. We will begin this project with a comprehensive study of all polyglutamylase enzymes, substrate and reaction specificity, subcellular localisation and tissue-specific expression, to finally find out the role of each enzyme. We then want to go into more details on specific functions of some of the glutamylases, beginning with the investigation of the role of polyglutamylation throughout the cell cycle. We are also interested in the enzymes that modify the centrioles of the centrosomes. In parallel, we develop new methods and materials, as the TTLL1-knock-out mouse that will allow us to study the role of polyglutamylation in neuronal cells later in the project. In conclusion, we hope to advance the perception of polyglutamylation and to maintain our present advantage of being the first who have discovered the enzymes.