A look at some relevant literature will show that the prevailing view certainly is that the hook is rotated by associated proteins in the basal body.
quote:
Flagellar movement driven by proton translocation.
Blair DF.
FEBS Lett. 2003 Jun 12;545(1):86-95.
The bacterial flagellar motor couples ion flow to rotary motion at high speed and with apparently fixed stoichiometry. The functional properties of the motor are quite well understood, but its molecular mechanism remains unknown. Recent studies of motor physiology, coupled with mutational and biochemical studies of the components, put significant constraints on the mechanism. Rotation is probably driven by conformational changes in membrane-protein complexes that form the stator. These conformational changes occur as protons move on and off a critical Asp residue in the stator protein MotB, and the resulting forces are applied to the rotor protein FliG.
One reference which I could only get the abstract for seems to suggest that the molecular mechanism is ratchet like, i.e the proton gradient drives a variety of conformational changes in the stator so the FliG or some such element connected to th MS ring is continuously in contact with some portion of the stator but moved in such a way, ratcheted, that it drives rotary motion of the flagella, which I would say is distinct from a freely rotating system. This mechanism would be similar to the cross-step mechanism in actin/myosin interactions.
quote:
Philos Trans R Soc Lond B Biol Sci. 2000 Apr 29;355(1396):491-501.
Constraints on models for the flagellar rotary motor.
Berg HC.
Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA
02138, USA. hberg@biosun.harvard.edu
Most bacteria that swim are propelled by flagellar filaments, each driven at its
base by a rotary motor embedded in the cell wall and cytoplasmic membrane. A
motor is about 45 nm in diameter and made up of about 20 different kinds of
parts. It is assembled from the inside out. It is powered by a proton (or in
some species, a sodium-ion) flux. It steps at least 400 times per revolution. At
low speeds and high torques, about 1000 protons are required per revolution,
speed is proportional to protonmotive force, and torque varies little with
temperature or hydrogen isotope. At high speeds and low torques, torque
increases with temperature and is sensitive to hydrogen isotope. At room
temperature, torque varies remarkably little with speed from about -100 Hz (the
present limit of measurement) to about 200 Hz, and then it declines rapidly
reaching zero at about 300 Hz. These are facts that motor models should explain.
None of the existing models for the flagellar rotary motor completely do so.
In this paper Berg describes a hypothetical cross-step mechanism.
quote:
Given the work of Blair and colleagues, I favour a
cross-bridge mechanism of the kind envisaged by Luger
(model II of Luger (1988)). In this scheme, proton trans-port
drives a cyclic sequence in which (i) a proton binds
to an outward-facing binding site (presumably, Asp32 of
MotB), (ii) the protonmotive force drives a conforma-tional
change, a power stroke (Berry & Berg 1999) that
moves the rotor forward (or stretches a spring that moves
it forward) and transforms the binding site to an inward-facing
site, and (iii) proton dissociation triggers detach-ment
of the cross-bridge from the rotor, its relaxation to
the original shape, and reattachment to an adjacent site.
If step (iii) is relatively fast, the cross-bridge will remain
attached to the rotor most of the time.
TTFN,
WK
P.S. My apologies if this is too extensive quoting.
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