It has been years since the observation of the dynamic instability of microtuble in mammalian cells. It was a great deal at that time! For sure, this is a very important feature of the tublin cytoskeleton, and is criticle for many things. However, another major cytoskeleton network - actin cytoskeleton, do not behave like microtuble. At least, right now, no evidence suggests that actin network has dynamic instability. Although, some people belive it exist. ParM is an ancient actin in E.coli, but it is not for constructing the cell network, but for precise plasmid seprartion. So, it has been shown that ParM filament has dynamic instability.
My theory is that one biochemical feature is designed for one functional job. The feature of filament dynamic instability is for precise genome separation (plasmid in E.coli, chromosome in mammalian cells). No matter it is actin filament or tubulin filament. The evolution always keep the function conserve, not the protein/protein name. What do you think?
the most recent paper talking about ParM
The EMBO Journal (2008) 27, 570–579, DOI: 10.1038/sj.emboj.7601978
Molecular structure of the ParM polymer and the mechanism leading to its nucleotide-driven dynamic instability
ParM is a prokaryotic actin homologue, which ensures even plasmid segregation before bacterial cell division. In vivo, ParM forms a labile filament bundle that is reminiscent of the more complex spindle formed by microtubules partitioning chromosomes in eukaryotic cells. However, little is known about the underlying structural mechanism of DNA segregation by ParM filaments and the accompanying dynamic instability. Our biochemical, TIRF microscopy and high-pressure SAX observations indicate that polymerization and disintegration of ParM filaments is driven by GTP rather than ATP and that ParM acts as a GTP-driven molecular switch similar to a G protein. Image analysis of electron micrographs reveals that the ParM filament is a left-handed helix, opposed to the right-handed actin polymer. Nevertheless, the intersubunit contacts are similar to those of actin. Our atomic model of the ParM-GMPPNP filament, which also fits well to X-ray fibre diffraction patterns from oriented gels, can explain why after nucleotide release, large conformational changes of the protomer lead to a breakage of intra- and interstrand interactions, and thus to the observed disintegration of the ParM filament after DNA segregation.
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