Abstract
BackgroundBacterial division is produced by the formation of a macromolecular complex in the middle of the cell, called the divisome, formed by more than 10 proteins. This process can be divided into two steps, in which the first is the polymerization of FtsZ to form the Z ring in the cytoplasm, and then the sequential addition of FtsA/ZipA to anchor the ring at the cytoplasmic membrane, a stage completed by FtsEX and FtsK. In the second step, the formation of the peptidoglycan synthesis machinery in the periplasm takes place, followed by cell division. The proteins involved in connecting both steps in cell division are FtsQ, FtsB and FtsL, and their interaction is a crucial and conserved event in the division of different bacteria. These components are small bitopic membrane proteins, and their specific function seems to be mainly structural. The purpose of this study was to obtain a structural model of the periplasmic part of the FtsB/FtsL/FtsQ complex, using bioinformatics tools and experimental data reported in the literature.ResultsTwo oligomeric models for the periplasmic region of the FtsB/FtsL/FtsQ E. coli complex were obtained from bioinformatics analysis. The FtsB/FtsL subcomplex was modelled as a coiled-coil based on sequence information and several stoichiometric possibilities. The crystallographic structure of FtsQ was added to this complex, through protein-protein docking. Two final structurally-stable models, one trimeric and one hexameric, were obtained. The nature of the protein-protein contacts was energetically favourable in both models and the overall structures were in agreement with the experimental evidence reported.ConclusionsThe two models obtained for the FtsB/FtsL/FtsQ complex were stable and thus compatible with the in vivo periplasmic complex structure. Although the hexameric model 2:2:2 has features that indicate that this is the most plausible structure, the ternary complex 1:1:1 cannot be discarded. Both models could be further stabilized by the binding of the other proteins of the divisome. The bioinformatics modelling of this kind of protein complex, whose function is mainly structural, provide useful information. Experimental results should confirm or reject these models and provide new data for future bioinformatics studies to refine the models.
Highlights
Bacterial division is produced by the formation of a macromolecular complex in the middle of the cell, called the divisome, formed by more than 10 proteins
The proposed FtsB/FtsL/FtsQ complex models are plausible because of the stability and the important number of hydrophobic residues accessible at the surfaces exposed to the solvent which could be available for the sequential interaction with the proteins of the peptidoglycan synthesis machinery
The very limited number of FtsQ molecules available for divisome formation in E. coli and the higher number of non-polar residues exposed to the solvent indicate that the trimeric FtsB/ FtsL/FtsQ models are in accordance with the expected complex in vivo
Summary
Bacterial division is produced by the formation of a macromolecular complex in the middle of the cell, called the divisome, formed by more than 10 proteins This process can be divided into two steps, in which the first is the polymerization of FtsZ to form the Z ring in the cytoplasm, and the sequential addition of FtsA/ZipA to anchor the ring at the cytoplasmic membrane, a stage completed by FtsEX and FtsK. In Escherichia coli, this process requires at least 12 essential proteins, localized at the constriction site at the cell equator These proteins coordinate the invagination of the cytoplasmic membrane and guide the inward growth of the peptidoglycan to produce the daughter cells. The proteins are recruited in the following order: FtsZ > FtsA/ZipA > FtsE/FtsX > FtsK > FtsQ > FtsB/FtsL > FtsW > FtsI > FtsN [3,4,5]. The recruiting mechanism, the binding characteristics, and the exact function of some of these proteins is still unknown
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