Biophysical Society Thematic Meeting - October 25-30, 2015

Polymers and Self Assembly: From Biology to Nanomaterials Poster Session I

18-POS Board 18 Filament Capping Regulates the Bacterial Tubulin-Like Cytoskeleton Bisson-Filho Alexandre 1 , Discola Karen 2 , Patricia Castellen 1,3 , Valdir Blasios 1 , Wanius Garcia 4 , Ana Carolina Zeri 3 , Harold Erickson 5 , Andrea Dessen 2,3 , Frederico Gueiros Filho 1 . 1 Instituto de Química - USP, São Paulo, Brazil, 2 Institut de Biologie Structurale, Grenoble, France, 3 Brazilian Biosciences National Laboratory (LNBio), Campinas, Brazil, 4 Centro de Ciências Naturais e Humanas, UFABC, Santo André, Brazil, 5 Duke University Medical Center, Durham, NC, USA. Cell division in bacteria is orchestrated by FtsZ, the tubulin ortholog of prokaryotes. At the time of division, FtsZ self assembles into a contractile protein structure, the Z ring, and this, in turn, remodels the bacterial envelope to achieve cytokinesis. Proteins that bind to FtsZ are key regulators of bacterial division and valuable probes for the understanding of the fundamental rules of FtsZ polymerization. Here we have applied biochemical and structural approaches to determine the mechanism of FtsZ inhibition by MciZ, a 40 amino acid peptide that shuts off cell division during spore development in Bacillus subtilis. The crystal structure of the FtsZ-MciZ complex was solved at 3.2 Å resolution and revealed that MciZ binds to the C-terminal polymerization interface of FtsZ, the equivalent of the minus end of tubulin. MciZ prevents the assembly of higher order FtsZ polymers at substoichiometric levels both in vitro and in vivo. This is not due to FtsZ monomer sequestration because FtsZ monomers self-poisoned with MciZ are as effective as MciZ alone at inhibiting FtsZ assembly. Furthermore, EM and fluorescence microscopy showed that MciZ binds to the ends of FtsZ filaments and shortens them. Thus, MciZ is an FtsZ filament capping protein, the first capping protein described for the bacterial cytoskeleton. Capping of the minus end is an unusual way of shortening filaments and indicates that fragmentation and annealing are important reactions for FtsZ filament assembly. The effect of MciZ on FtsZ dynamics also indicates that FtsZ filaments exhibit the same polarity as microtubules and, thus, could undergo treadmilling.

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