Our research focus on the human pathogen Helicobacter pylori. We have three main subjects:
Bacterial cell division is a highly organized process mediated by the dynamic action of a molecular machinery called the divisome. The main step in formation of this divisom is polymerization of the tubulin homologue FtsZ, which assembles into the Z-ring. In many bacteria, positioning of the Z-ring involves negative regulators of FtsZ that prevent its polymerisation in all cellular regions except at midcell: In E. coli, the MinCDE system helps to localize the Z-ring to the cell centre by inhibiting its assembly at the poles. In C. crescentus FtsZ is clustered at one single cell pole before it is induced to assemble at mid-cell, a process that is regulated by MipZ, a ParA-like protein, that directly inhibit FtsZ polymerization. Generally ParAB systems are central compounds connecting replication and segregation in many bacteria. However, there exist ParA-like proteins implicated with different developmental processes. In C. Glutamicum, the orphan parA-like gene codes for a protein designated PldP (ParA-like division protein), which might act as a septum inhibitor. In contrast, the ParA-like protein PomZ of Myxoxoccus xanthus is part of a protein system that is important for Z-ring formation by positively regulating recruitment of FtsZ to midcell.
With respect to cytokinesis, the ε-proteobacteria remain one of the most understudied bacterial lineages. Only recently, we have shown that the mode of cell division of H. pylori is clearly distinct from that of the model organisms E. coli, B. subtilis, and C. crescentus. Despite of having the regulatory MinCDE system, the key factor of cell division, FtsZ, localizes in a novel pattern (Specht et al., 2013). In H. pylori cell expressing FtsZ-GFP distinct fluorescent foci are present at one in small cells (i.e. young cells) just after completed cell division. Later in the cell cycle, FtsZ-rings are positioned with very little precision with half of the cells showing clearly asymmetrically localized FtsZ-rings. Even in cells with an apparently mid-cell Z-ring there was 10% variation of Z-ring positioning, which is much larger than the at most 5% variation observed in E. coli or B subtilis (Specht et al., 2013) This process resulted in H. pylori daughter cells having considerably different sizes. Thus, we suggest a model of cell division in H. pylori in which FtsZ accumulates at one cell pole after a complete cell division and then starts moving from this pole to the next localization of cell division, building up the Z ring. Thereby, the FtsZ ring is positioned with little precision, such that central as well as acentral rings can be observed (figure). Daughter cells showed considerably different sizes, suggesting that H. pylori divides asymmetrically.
Specht M, Dempwolff F, Schätzle S, Thomann R, Waidner B. Localization of FtsZ in Helicobacter pylori and consequences for cell division. J Bacteriol. 2013 Apr;195(7):1411-20
In H. pylori both the spiral cell morphology and the polar bundle of flagella contribute to the motility of H. pylori. Motility is a key factor of infection, allowing for penetration of the mucus and enabling the bacteria to colonize and to persist in the gastric lumen. Although the flagella of H. pylori have been studied intensively, the knowledge of the establishment and the maintenance of its spiral structure is still marginal. Recent research revealed that it is apparently controlled by two unrelated mechanisms that operate at different levels: peptidases influence cell shape by causing peptidoglycan relaxation, whereas we demonstrated that so-called coiled-coil-rich proteins (Ccrp) compose an intracellular scaffold influencing cell shape.
H. pylori contains four Ccrps (Ccrp58, Ccrp59, Ccrp1143, and Ccrp1142) spontaneously polymerizing in the absence of any cofactor in vitro (Waidner et al., 2009; Specht et al., 2011). Deletion of ccrp59 results in the complete loss of helical cell shape, while inactivation of other ccrps affects cell morphology to a lesser extent and in varying ways, depending on the strain background. Ccrp59-GFP localized in a punctate/patchy pattern, with several static foci distributed along the long-axis of the cell, suggestive of helical filaments. Similar to crescentin, the H. pylori Ccrp cytoskeleton may thus serve to mechanically reduce the rate of peptidogylcan biosynthesis within a region that winds helically around the cell cylinder, thus leading to deformation of the peptidoglycan sacculus. Alternatively, it could modulate cell shape more directly by controlling the positioning of cell wall biosynthetic enzymes, but information on potential interaction partners is still missing.
Specht M, Schätzle S, Graumann PL, Waidner B. Helicobacter pylori possesses four coiled-coil-rich proteins that form extended filamentous structures and control cell shape and motility. J Bacteriol. 2011 Sep;193(17):4523-30.
Waidner B, Specht M, Dempwolff F, Haeberer K, Schaetzle S, Speth V, Kist M, Graumann PL. A novel system of cytoskeletal elements in the human pathogen Helicobacter pylori. PLoS Pathog. 2009 Nov;5(11):e1000669.
In most cells the cytoskeletal proteins form a dynamic self-organizing system. This also applies the coiled coil rich proteins of H. pylori as the proteins could be purified as soluble self assembling proteins, which were able to build large polymers and sheets (Waidner et al., 2009; Specht et al., 2011). Such polymers or sheets might be useful as scaffolds in or outside of cells.
Therefore a long term goal of our group is to explore and exploit the formative capability of these proteins for synthetic biological purposes e.g. in metabolic engineering. To this end we are now characterizing biochemical and biophysical properties of H. pylori Ccrps. In this regard we already have seen that the sheet forming properties of Ccrp59 fused to one protein still remain (figure).