Lotte Søgaard-Andersen

Lotte Søgaard-Andersen

Prof. Dr. Lotte Søgaard-Andersen

Max Planck Institute for Terrestrial Microbiology
Karl-von-Frisch-Straße 10, 35043 Marburg
+49-6421 178 201


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Research project within SYNMIKRO

Similarly to eukaryotic cells bacterial cells are also spatially highly organized and display polarity with individual chromosomal loci, mRNA’s, proteins, and lipids localizing to specific subcellular regions. Moreover, several proteins localize dynamically and change localization pattern over time. For most dynamically localized proteins, the localization pattern changes in a cell cycle dependent manner. An exception to this general rule are motility proteins in Myxococcus xanthus that localize dynamically to the cell poles in a cell cycle-independent manner, i.e. during a cellular reversal motility proteins localizing to the lagging cell pole switch to the new lagging cell pole and proteins and the leading cell pole switch to the new leading cell pole. The goal of this project is to identify and characterize the components of the regulatory system that underlies the dynamic polarity of motility proteins in M. xanthus. On the basis of this system, we long term aim to define a minimal module for regulation of dynamic cell polarity in bacteria and to establish this system in other microorganisms as well as in synthetic cells.

Figure 1. The motility proteins AglZ (green) and RomR (red) localize to opposite poles; Figure 2. MglB-YFP localizes dynamically to the lagging cell pole.; Figure 3. Schematic of the model for how MglA and MglB together with the Frz system define the leading/lagging cell pole polarity axis.

The regulatory system that controls polarity in M. xanthus is built around the MglA and MglB proteins, which define the leading/lagging pole polarity axis. MglA is a small Ras-like GTPase that functions as a nucleotide-dependent molecular switch to regulate motility in M. xanthus. The MglB protein functions as a GTPase activating protein (GAP) and converts active MglA/GTP to the inactive MglA/GDP. Between reversals MglA/GTP localizes to the leading cell pole while MglB localizes to the lagging cell pole. The two proteins bind to the two poles in a mutually exclusive manner and define the leading/lagging pole polarity axis. Our data suggest that MglA/GTP between reversals sets up the correct polarity of dynamically motility proteins. In response to signaling activity of the Frz chemosensory system MglA/GTP is released from the leading pole and relocates to the old lagging cell pole and as a consequence, MglB relocates to the old leading pole. In total, this results in an inversion of the leading/lagging pole polarity axis and the relocation of dynamic motility proteins.

 Figure 4. 3D structure of MglA in the GDP- (left) and GTP-(right) bound form. MglA undergoes a dramatic, GDP–GTP-dependent conformational change involving a screw-type forward movement of the central β2-strand (orange), not previously observed in a small GTPase. This movement and complex formation with MglB repositions the conserved residues Arg53 (turquoise) and Gln82 (green) into the active site.

SYNMIKRO Young Researchers Groups

Almost all scientific members of SYNMIKRO are actively involved in DFG’s Collaborative Research Centers (Sonderforschungsbereiche), Research Training Groups (Graduiertenkollegs), or other Cooperative Research projects. Alongside performing adventurous experiments, and reporting excellent science, SYNMIKRO substantially promotes potential Young Research Group Leaders by constantly keeping its doors open to welcome and support Young Researchers planning to set up an Independent Research Group.
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