Insights into initial stages of bacterial cell division: Looking at dynamic FTSZ polymers on surfaces at the nanoscale

Seminar

Title: Insights into initial stages of bacterial cell division: Looking at dynamic FTSZ polymers on surfaces at the nanoscale
Speaker: Marisela Vélez
Affiliation: Instituto de Catálisis y Petroleoquímica CSIC, Madrid

Abstract

Insights into initial stages of bacterial cell division: Looking at dynamic FTSZ polymers on surfaces at the nanoscale

Mario Encinar del Pozo1, Pablo Mateos-Gil1, Ileana Márquez1, Marisela Vélez 1,2
1 Instituto de Catálisis y Petroleoquímica, c/Marie Curie 2, Cantoblanco, Madrid 28049
2 IMDEA NanocienciaFacultad de Ciencias Módulo C-IX, 3ª planta,Avda. Fco. Tomás y Valiente, 7, Cantoblanco, Madrid 28049

Some of the most interesting biological self assembling materials are the cytoskeletal proteins. They are soluble proteins that can polymerize in a reversible manner when exposed to a soluble nucleotide. The nanometer individual units assemble into micrometer long dynamic structures that perform different mechanical or structural functions.
The bacterial protein FtsZ is a soluble GTPase structurally analogous to eukaryotic tubulin and in vivo it assembles on the inner side of the cytoplasmic membrane in the mid region of the bacteria at the time of cell division. The protein self-organizes on the surface after binding to a protein membrane anchor, protein ZipA in the case of E. coli, and triggers the cell division process. It contributes to the recruitment of other proteins participating in forming the protein complex called the divisome. The polymer formed also participates in the force generating process that divides the cell [1].
The characterization of the structure and dynamics of in vitro polymerization of FtsZ on mica with atomic force microscopy has provided information about how individual filaments interact to form higher order aggregates [2]. This high resolution information has been analyzed theoretically to help identify relevant interactions governing the behavior [3]. The study of the polymer behavior on lipid membranes of different composition, using the membrane protein ZipA as the anchor to mimic the situation found in vivo, has revealed a large polymorphism in the structures formed and the sensitivity of their shape to the underlying lipid composition as well as to the structure and orientation of the anchoring protein [4].
In order to further understand the observed polymorphism and to gain deeper insight into the importance of the protein orientation and interaction with the surface, we have also explored alternative ways of anchoring the protein to lipid surfaces. Orienting genetically modified FtsZ proteins* by covalent linkage to lipids included in a fluid two dimensional membrane provides two main advantages: restricting the orientation of the polymerizing units on the surface and allowing them to diffuse to explore the most favorable interactions. We found that the shape of the polymer assemblies on the surface is greatly dependent on the orientation of the individual monomers on the lipid membrane, revealing that other monomer-monomer interaction regions, aside from the longitudinal interactions favored by the presence of GTP, are relevant for the formation of higher order filament aggregates and could therefore also play a role in the formation of the FtsZ polymers active during cell division.

* kindly provided by Miguel Vicente ( CNB, CSIC) and Germán Rivas ( CIB, CSIC)

[1] Vicente,M., Rico, A. I., Martínez-Arteaga,R. and Mingorance, J. (2006) J of Bacteriology 188, 19–27
[2] Mingorance, J. ; Tadros , M.; Vicente, M. ; González , J. M.; Rivas , G. and Vélez, M. (2005) J. Biol.Chem. , 280, 20909–20914.
[3] Paez , A., Mateos-Gil , P. Hörger,I, Mingorance ,J. Rivas , G. Vicente ,M. Vélez, M. and Tarazona, P (2009) PMC Biophysics, 2:8
[4] López Navajas, P., Rivas, G. , Mingorance, J., Mateos-Gil,P, Hörger,I, Velasco, E. , Tarazona, P and Vélez,M. J Biol Phys (2008) 34:237–247