Extreme C Terminus of Bacterial Cytoskeletal Protein FtsZ Plays Fundamental Role in Assembly Independent of Modulatory Proteins

Paul J Buske,Petra Anne Levin

doi:10.1074/jbc.m111.330324

Paul J Buske, Petra Anne Levin

Open Access

https://doi.org/10.1074/jbc.m111.330324

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Abstract

Bacterial cell division typically requires assembly of the cytoskeletal protein FtsZ into a ring (Z-ring) at the nascent division site that serves as a foundation for assembly of the division apparatus. High resolution imaging suggests that the Z-ring consists of short, single-stranded polymers held together by lateral interactions. Several proteins implicated in stabilizing the Z-ring enhance lateral interactions between FtsZ polymers in vitro. Here we report that residues at the C terminus of Bacillus subtilis FtsZ (C-terminal variable region (CTV)) are both necessary and sufficient for stimulating lateral interactions in vitro in the absence of modulatory proteins. Swapping the 6-residue CTV from B. subtilis FtsZ with the 4-residue CTV from Escherichia coli FtsZ completely abolished lateral interactions between chimeric B. subtilis FtsZ polymers. The E. coli FtsZ chimera readily formed higher order structures normally seen only in the presence of molecular crowding agents. CTV-mediated lateral interactions are important for the integrity of the Z-ring because B. subtilis cells expressing the B. subtilis FtsZ chimera had a low frequency of FtsZ ring formation and a high degree of filamentation relative to wild-type cells. Site-directed mutagenesis of the B. subtilis CTV suggests that electrostatic forces are an important determinant of lateral interaction potential.

Highlights

Of the cytoskeletal protein FtsZ into a loose bundle of filaments at the nascent septum initiates bacterial cell division
Transmission electron micrographs of 3 ␮M FtsZ assembled in our standard FtsZ polymerization buffer (50 mM MES, pH 6.5, 50 mm KCl, 2.5 mM MgCl2, 1 mM EGTA, 1 mM GTP) indicate that B. subtilis FtsZ (Bs FtsZ) has a strong propensity to form stable lateral interactions, whereas E. coli FtsZ (Ec FtsZ) does not (Fig. 2)
B. subtilis FtsZ C-terminal variable (CTV) Is Sufficient to Induce Lateral Interactions between FtsZ Protofilaments—Based our finding that the C terminus of Bs FtsZ was required for lateral interactions in vitro, we investigated the role of the CTV in this process

Summary

Background

Of the cytoskeletal protein FtsZ into a loose bundle of filaments at the nascent septum initiates bacterial cell division. Results: The extreme C terminus of FtsZ mediates electrostatic interactions between FtsZ polymers. Bacterial cell division typically requires assembly of the cytoskeletal protein FtsZ into a ring (Z-ring) at the nascent division site that serves as a foundation for assembly of the division apparatus. Several proteins implicated in stabilizing the Z-ring enhance lateral interactions between FtsZ polymers in vitro. We report that residues at the C terminus of Bacillus subtilis FtsZ (C-terminal variable region (CTV)) are both necessary and sufficient for stimulating lateral interactions in vitro in the absence of modulatory proteins. CTV-mediated lateral interactions are important for the integrity of the Z-ring because B. subtilis cells expressing the B. subtilis FtsZ chimera had a low frequency of FtsZ ring formation and a high degree of filamentation relative to wild-type cells.

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EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION