Septins: comparative studies and the correlation between structure and function

Abstract

The present proposal focuses on structural and functional aspects of the septin family of proteins using an integrated approach involving a series of biophysical and cellular techniques. Despite having been described for the first time 40 years ago in yeast, where they are essential for completing the cell cycle, septins are still considered a neglected component of the cytoskeleton in terms of their biochemistry and physiology. For example, little is known concerning the factors which control the formation of a septin hetero-filament and how this is related to GTP binding, GTP hydrolysis and membrane association. Furthermore, only one crystal structure of the dozens of possible combinations for a hetero-filament has been described to date, and that at low resolution. Even less is known about septins from lower organisms. The current research proposal is divided into three sub-projects dealing respectively with structural, functional and evolutionary aspects of septins from different organisms: humans, a helminth, a cephalochordate and an alga. In structural terms we propose visualizing directly filaments and proto-filaments using electron microscopy as well as resolving crystal and NMR structures of individual septins and their hetero-complexes, and individual domains in the presence of ligands such as GTP, GDP and Mg2+. These results will be complemented by functional studies which aim to identify, for example, binding partners for the unique septins from a green algae and the mechanisms behind the septin-inhibitor induced paralysis of Schistosoma mansoni. (AU)