Lotte Sogaard-Andersen
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Bacterial development and differentiation
Regulation of cell polarity
About 30 years ago, the laboratory of Prof. Dale Kaiser at Stanford University showed that the MglA protein is important for the function of both motility systems in M. xanthus. MglA is a member of the Ras-superfamily of G-proteins. In eukaryotic cells several members of this superfamily of proteins function as nucleotide-dependent molecular switches to regulate cell polarity. Therefore, we hypothesized that MglA could be involved in setting up and regulating the polarity of motility proteins. Recently, we were able to show that MglA acts as a nucleotide-dependent molecular switch to regulate motility and that MglB, which is encoded in an operon with MglA, represents a novel GTPase-activating protein (GAP) family and is the cognate GAP of MglA. Between reversals, MglA/GTP is restricted to the leading and MglB to the lagging pole defining the leading/lagging polarity axis. For reversals, the Frz chemosensory system induces the relocation of MglA/GTP to the lagging pole causing an inversion of the leading/lagging polarity axis. MglA/GTP stimulates motility by establishing correct polarity of motility proteins between reversals and reversals by inducing their pole-to-pole relocation. Thus, the function of Ras-like G-proteins and their GAPs in regulating cell polarity is found not only in eukaryotes, but also conserved in bacteria. We are currently focusing on identifying downstream effectors of MglA/GTP to understand how MglA/GTP brings about the correct localization of motility proteins.
Temporal and spatial regulation of MglA activity by Frz and MglB