Structural insight into FtsZ polymer dynamics

Maria A Oliva-Blanco

FtsZ is an essential bacterial protein involved in cell division through the formation of a polymeric ring structure that is the framework for assembly of other components of the division machinery. Despite of the limited similarity sequence identity between FtsZ and eukaryotic tubulin, their structures showed that they share a common fold and form a new group of GTPases proteins.

Comparison of tubulin structures obtained in different states has lead to a model in which the tubulin monomer undergoes a conformational switch between a "straight" form found in the wall of the microtubbules (tubulin polymerized state) and a "curved" form associated with depolymerization. I have been working on crystal structure determination of FtsZ in presence of Aluminium Fluoride and GDP (to understand the transition state of the nucleotide gamma phosphate during GTP hydrolysis) and with different GTPase inhibitors to obtain information of the conformational change in the protein. During my EMBO Long Term Fellowship I have been able to solve 3 new FtsZ structures from Bacillus subtilis (BsFtsZ), Methanococcus jannaschii Pseudomonas aeruginosa (PaFtsZ).

MjFtsZ structure in presence of AlF4- haven't revealed any information about the transition state because the absence of Aluminium Fluoride in the electron density map, but this structure, at 1.7A, show the highest resolution FtsZ structure at the moment.

Superposition of PaFtsZ, in complex with bacteria cell inhibitor SulA and a previous MjFtsZ revealed differences that were reminiscent of the curved-to-straight conformational switch thought to occur in tubulin due to SulA binding to FtsZ bottom surface. SulA-free PaFtsZ new structure revealed no differences with SulA-bound FtsZ as it was expected. By comparing by bioinformatics tools the full range of FtsZ structures determined in different crystal forms and nucleotide states and in presence and absence of regulatory proteins, I surprisingly have found no evidence of a conformational change involving domain movement because GTP hydrolysis as it occur in other GTPases proteins. Therefore FtsZ show a high flexibility with inter-species differences in domain orientation. Due to these observations I have propose a new model in which lateral interactions during polymerization help to determine the curvature of protofilaments. These results have been compile in a manuscript entitle ˜Structural Insights into the Conformational Variability of Fts", which was recently sent.