Post details: Explaining structural similarities in molecular motors

01/06/07

Permalinkby 09:29:00 am, Categories: Literature - Articles, 399 words   English (UK)

Explaining structural similarities in molecular motors

Close examination of the bacterial flagellum motor and the ATPsynthase motor reveals many similarities, sufficient (say the authors) to “imply an evolutionary relation between the flagellum and F0F1-ATPsynthase and a similarity in the mechanism between FliI and F1-ATPase despite the apparently different functions of these proteins”.
But is structural similarity a defining mark of an evolutionary relationship? On this basis, the octopus eye has to have an evolutionary relationship with the mammalian eye. Examples described as convergent evolution abound, and in these cases Darwinians invoke natural selection as the driver. Why is this not an option for molecular machines? The authors are so familiar with these complex systems that they know the absurdity of the convergence option: with parallel incremental changes under the influence of selection forces.
So, an “evolutionary relationship” is the only option – or is it? Structural similarities due to intelligent design should also be evaluated as a hypothesis (but is rarely even considered as an option because naturalism is the dominant philosophy in science).

Structural similarity between the flagellar type III ATPase FliI and F1-ATPase subunits
Katsumi Imada, Tohru Minamino, Aiko Tahara, and Keiichi Namba
Proc. Natl. Acad. Sci. USA, Published online before print January 3, 2007, doi: 10.1073/pnas.0608090104

Abstract: Construction of the bacterial flagellum in the cell exterior proceeds at its distal end by highly ordered self-assembly of many different component proteins, which are selectively exported through the central channel of the growing flagellum by the flagellar type III export apparatus. FliI is the ATPase of the export apparatus that drives the export process. Here we report the 2.4 Å resolution crystal structure of FliI in the ADP-bound form. FliI consists of three domains, and the whole structure shows extensive similarities to the α and β subunits of F0F1-ATPsynthase, a rotary motor that drives the chemical reaction of ATP synthesis. A hexamer model of FliI has been constructed based on the F1-ATPase structure composed of the α 3 β 3 γ subunits. Although the regions that differ in conformation between FliI and the F1- α / β subunits are all located on the outer surface of the hexamer ring, the main chain structures at the subunit interface and those surrounding the central channel of the ring are well conserved. These results imply an evolutionary relation between the flagellum and F0F1-ATPsynthase and a similarity in the mechanism between FliI and F1-ATPase despite the apparently different functions of these proteins.

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