June 12, 2010 | David F. Coppedge

Flagellum Replaces Parts on the Fly

A new study appears to show that the bacterial flagellum, a molecular rotary motor that has become iconic of the intelligent design movement, can repair parts of its rotor while it is rotating.  The results of the study by Oxford University were published in PNAS,1 and were also the focus of a Commentary in PNAS by Michael D. Manson of Texas A&M University.2  Previous studies had shown that parts of the stationary part (stator) could be replaced while the flagellum was in operation, but the rotor?  “Turnover of a component of the rotor is even more surprising than stator turnover, given that it was previously known that the number of stator complexes can change while the motor is running,”  the Oxford scientists said.  The abstract explained:

Most biological processes are performed by multiprotein complexes.  Traditionally described as static entities, evidence is now emerging that their components can be highly dynamic, exchanging constantly with cellular pools…. It is powered by transmembrane ion flux through a ring of stator complexes that push on a central rotor.  The Escherichia coli motor switches direction stochastically in response to binding of the response regulator CheY to the rotor switch component FliM.  Much is known of the static motor structure, but we are just beginning to understand the dynamics of its individual components…. We show that the ~30 FliM molecules per motor exist in two discrete populations, one tightly associated with the motor and the other undergoing stochastic turnover…. In many ways the bacterial flagellar motor is as an archetype macromolecular assembly, and our results may have further implications for the functional relevance of protein turnover in other large molecular complexes.

“The bacterial flagellar motor is one of the most complex biological nanomachines,” began the first sentence of their paper, edited by Howard Berg (Harvard), one of the pioneers of flagellum research.  Using specialized imaging techniques, the Oxford team was able to identify components of the rotor complex undergoing dynamic turnover in about 30- to 40-second timeframes.  This turnover may be due to maintenance of the motor, or it may have functional significance.  It may be involved, for instance, in switching the rotation from normal counterclockwise runs to the occasional clockwise “tumbling” that bacteria undergo when following a chemical trail.  In E. coli, which have four to eight flagella, it may be involved in synchronization of the flagella – they don’t yet know for sure.  It appears that signaling from the environment is involved in the turnover, because a response regulator in the chemotaxis signal transduction response pathway “is also required for measurable FliM turnover to occur over the time scale of our experiments,” they said.  Though not certain whether it is a trigger or a by-product of the switch from normal mode to tumbling mode, the association is compelling: “This work represents direct evidence for signal-dependent dynamic exchange of switch complex components in functioning flagellar motors, raising the possibility that turnover is involved in the signaling mechanism.”
    Michael Manson commented on the findings in PNAS,2 offering additional interesting details about the flagellum: “The flagellar motor was the first biological rotary device discovered” (Berg, 1973), he pointed out; “Flagella spin at several hundred to >1,000 revolutions per second in different bacteria.”  He described the parts list and something about the torque and operation of the flagellum, and provided a cross-sectional diagram.  “Filament growth decreases with length, and a broken filament can regenerate,” he continued.  “Unfolded flagellin subunits diffuse through the hollow center of the filament and assemble at its distal tip.  Filaments extend several cell lengths and are quite fragile; their dynamic nature is necessary.  Each flagellar motor functions for the lifetime of its cell.”  He described how protons flow through the Mot complexes (parts of the stator) and then couple to the rotor, and how these must be firmly anchored to the cell wall to endure the tremendous torques put on them by the rotor: “The high torque required to turn a flagellum under heavy load requires that Mot complexes attach firmly to the cell wall.”   Even so, “Despite its anchoring, the stator is surprisingly dynamic.”  Other studies show that the Mot protein parts also turnover rapidly – with a half-life of 30 seconds.
    As for the findings of the Oxford team, Manson said, “Parts exchange in the stator and rotor may just be routine maintenance, and the aggregates of 18 FliM molecules could be storage devices rather than assembly intermediates.  The authors are suitably cautious about speculating whether FliM turnover is involved in the switch function of the C ring, emphasizing that the exchange of FliM subunits could be either a cause or effect of motor reversal.”  But as he looked forward to additional exciting findings in this kind of research on flagella and other molecular machines, he paid his respects to this machine in particular: “Further studies of this type will undoubtedly lead to exciting new revelations about the inner workings of the elegant molecular machinery of the flagellar motor.

1.  Delalez et al, “Signal-dependent turnover of the bacterial flagellar switch protein FliM,” Proceedings of the National Academy of Sciences, Published online before print May 24, 2010, doi: 10.1073/pnas.1000284107.
2.  Michael D. Manson, “Dynamic motors for bacterial flagella,” Commentary, Proceedings of the National Academy of Sciences, print June 11, 2010, doi: 10.1073/pnas.1006365107.

Altogether now, shout the familiar refrain: “These authors said nothing about evolution!”  If nothing in biology makes sense except in the black-light of ev-illusion, where was Mr. Darwin?  Is that him in bed, sick to his stomach again?  Go make him some intelligently designed chicken soup, and leave him be.  The rest of us are excited about the union of engineering and biology in this clear case of machinery on the molecular scale.  Now we have an example of possible maintenance during operation, and if not that, a functional operation that involves dynamic swapping of parts while a rotor is spinning at more than 60,000 rpm!  The bacterium doesn’t need to go into a drydock; its repair squad can fix parts on the fly.  Imagine what would be required to swap out the blades on an outboard motor while it is spinning.  Furthermore, imagine having the process automated, with feedback from the environment.  How would you even design such a thing?  The flagellum has a constant flow of FliM parts into the system.  Apparently, there is some sort of buffer store where parts can stand ready for use, and then something guides them into position.  Manson’s oversimplified diagram shows a part attaching to a rotor blade, which might provide an attachment point for a FliM molecule to get replaced during a reversal of direction.  However this occurs, it is bound to be exciting and amazing.
    Did you catch that dramatic understatement by Manson?  “Parts exchange in the stator and rotor may just be routine maintenance, and the aggregates of 18… molecules could be storage devices….”  What did he just say?  Maintenance!  Storage devices!  This is bacteria we are talking about.  This is life that lives in dirty water.  That’s like walking by a mud puddle and saying, “The murkiness down there could just be routine automated guidance and control operations with robotic feedback software, and the squiggles could be gigabytes of storage area networks with rapid retrieval, but hey.  Whatever.  Oh, and there’s a maintenance crew that can swap out outboard motor blades on the fly, too.  Stickagum, man?”
    Get the picture here, folks – these are cells that in Darwin’s day were thought to be made of undifferentiated blobs of jelly-like stuff.  For lack of a better word to describe it, they called it by the suggestive pantheistic term, “protoplasm” (first living substance).  Anybody who thinks that way now with what molecular biology has revealed should get 39 lashes with a wet flagellum.  Evolution was missing from these papers because it is bankrupt.  It thrived in another age, another time, when puffed-up, imperialistic, progress-minded Victorians didn’t know better.  This is the information age.  The only theory with the vocabulary, concepts and explanatory resources to deal with observations that are rich in engineering, machinery and control language is intelligent design.

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