[asa] Reducible complexity

The latest Science has an article about removing some parts from a
biochemical motor and finding that it still works, though not as well:

Axle-Less F1-ATPase Rotates
in the Correct Direction
Shou Furuike,1* Mohammad Delawar Hossain,1,2* Yasushi Maki,3
Kengo Adachi,1 Toshiharu Suzuki,4,5 Ayako Kohori,1 Hiroyasu Itoh,6,7
Masasuke Yoshida,4,5 Kazuhiko Kinosita Jr.1†
F1–adenosine triphosphatase (ATPase) is an ATP-driven rotary molecular
motor in which the central g subunit rotates inside a cylinder made of
three a and three b subunits alternately arranged. The rotor shaft, an
antiparallel a-helical coiled coil of the amino and carboxyl termini
of the g subunit, deeply penetrates the central cavity of the stator
cylinder. We truncated the shaft step by step until the remaining
rotor head would be outside the cavity and simply sat on the concave
entrance of the stator orifice. All truncation mutants rotated in the
correct direction, implying torque generation, although the average
rotary speeds were low and short mutants exhibited moments of
irregular motion. Neither a fixed pivot nor a rigid axle was needed
for rotation of F1-ATPase.

SCIENCE VOL 319 15 FEBRUARY 2008 p. 955

If the intermediate steps are useful, even though they do not provide
the full function of the final product, then they can be selected for.

-- 
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
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