Nucleation and polymerization of MreB, the bacterial otholog of actin

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Actin plays several key roles in many cellular aspects of eukaryotic cells. Many prokaryotic cells contain a close relative of actin, called MreB, which shares many conserved properties with actin, and is also essential for viability in many bacteria. Thus, actin and MreB have originated from an evolutionarily ancient filament-forming protein, which has diverged to fulfil an amazing spectrum of dynamic as well as static functions in all kinds of cells. Bacillus subtilis MreB is studied as a model for prokaryotic MreB proteins, and has been shown to be essential for cell cycle progression and for cell shape maintenance. We have found that it localizes as dynamic helical filaments underneath the cell membrane, which appear to extend/retract by a ratchet-like mechanism. Now we are able to study the polymerization of MreB in vitro, having generated a functional strep-tag version. Within the proposed consortium, we plan to study nucleation and extension properties of MreB filaments, because information on the prokaryotic counter part of actin will shed important light onto the evolutionary conserved properties of this protein. We have found that MreB interacts with translation elongation factor EF-Tu, which affects filamentation properties, and want to further study this important interaction. We have found that the three B. subtilis MreB paralogs have strikingly different filament architectures, and plan to dissect this unique phenomenon by mutagenesis and a variety of techniques available within the SPP 1464 consortium.