November 8, 2006 | David F. Coppedge

Bacterial Flagellum Multitasking and Assembly Described

Since the bacterial flagellum has become a de facto icon of the intelligent design movement, it’s instructive to see what new discoveries come to light on the molecular machine par excellence.  Two papers appeared recently.

  1. Ferry Boats:  A Cambridge team publishing in PNAS1 studied how the parts get to the assembly site.  The studied one of the many flagellum proteins, FliJ:

    We reveal that the essential export protein FliJ has a novel chaperone escort function in the pathway, specifically recruiting unladen chaperones for the minor filament-class subunits of the filament cap and hook-filament junction substructures….  The data show that FliJ recruits chaperones and transfers them to subunits, and indicate that this is driven by competition for a common binding site.  This escort mechanism provides a means by which free export chaperones can be cycled after subunit release, establishing a new facet of the secretion process.  As FliJ does not escort the chaperone for the major filament subunit, cycling may offer a mechanism for export selectivity and thus promote assembly of the junction and cap substructures required for initiation of flagellin polymerization.

  2. Slogan spin:  “Thanks to the new work of Murphy et al., we now have a view of the bacterial flagellum in situ and quick-frozen in time as if a flash bulb had stopped its action.”  David DeRosier wrote this in Current Biology2 in response to the paper mentioned here on 09/01/2006.  DeRosier included two of the stunning new 3D models of the intricacies of the rotor and stator.  Two other sample images can also be found at Caltech E&S (Volume LXIX, Number 3, 2006, p. 6), recently released for publication.
        DeRosier’s opening sentences confirm statements made in the film Unlocking the Mystery of Life:

    The flagellum, with its complexity of structure and multiplicity of function, is a machine that boggles the mind.  While musing on possible phrases that might catch the reader’s attention, I was reminded of the memorable 1926 slogan for the Hoover vacuum cleaner: “It beats as it sweeps as it cleans.”  The flagellum self-assembles as it propels as it responds; that is, the flagellum not only pushes the cell along, it also responds to intracellular signals and it assembles itself.  It seems as amazing as the old Hoover did in its heyday.  But, I thought, the bacterial flagellum does not really ‘beat’; the eukaryotic flagellum, an entirely different machine, does that.  Instead, the prokaryotic flagellum spins, driven by a rotary motor at speeds of over 100,000 rpm in at least one species.  The torque generated by the motor is converted to thrust by the corkscrew-shaped filament or propeller (for a review see [4]).
        Of the 40 genes needed to code for a flagellum, at least 24 produce proteins found in the final structure….

    After describing the wonders of this machine, DeRosier once again found inspiration in commercials: “Let us end with another familiar slogan but this time applied to the tomograms of the flagellum: ‘It’s the real thing.’”

1Evans et al, “An escort mechanism for cycling of export chaperones during flagellum assembly,” Proceedings of the National Academy of Sciences USA, 10.1073/pnas.0605197103, published online before print November 6, 2006.
2David DeRosier, “Dispatch: Bacterial Flagellum: Visualizing the Complete Machine In Situ,” Current Biology, Volume 16, Issue 21, 7 November 2006, Pages R928-R930, doi:10.1016/j.cub.2006.09.053.
3Y. Magariyama, S. Sugiyama, K. Muramoto, Y. Maekawa, I. Kawagishi, Y. Imae and S. Kudo, “Very fast flagellar rotation,” Nature 371 (1994), p. 752.

Finally we found a source corroborating the claim made in the film that some of these flagella can rotate at 100,000 rpm.  Most sources mention much lower (though still impressive) values of around 18,000 rpm.  DeRosier cites a case in the 102,000 rpm range; we will reproduce this source as footnote 3 above for those interested.3
    None of the three sources cited in the entry above mention evolution.  We have to keep saying that.  None of them, either, mentioned the fact that it is the intelligent design community that has brought these molecular machines to the attention of the public as examples of biological structures that defy Darwinian explanations.  They’d rather not touch that subject with a ten-foot propeller.
    They should, though.  The more young people watching Unlocking the Mystery of Life, the more might become interested in science.  The more scientists interested in these molecular machines, the more funding might become available.  This is another way ID can stimulate scientific research.  What’s Darwin got to do with it?  Nothing but spin doctoring.

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