October 27, 2004 | David F. Coppedge

Bacterial Flagellum Reveals New Structural Complexity

The bacterial flagellum, the unofficial mascot of the Intelligent Design movement, got more praise from the evolutionary journal Nature this week: Samatey et al.1 analyzed the hook region in detail and found that it is composed of 120 copies of a specialized protein that “reveals the intricate molecular interactions and a plausible switching mechanism for the hook to be flexible in bending but rigid against twisting for its universal joint function.
    Christopher Surridge, commenting on this paper in the same issue,2 adds that this joint must be able to bend up to 90 degrees in a millisecond or less while rotating at up to 300 times per second.  He says that the researchers describe “how they determined the atomic structure of this super-flexible universal joint, and thereby how it achieves such a feat of engineering.

1Samatey et al., “Structure of the bacterial flagellar hook and implication for the molecular universal joint mechanism,” Nature 431, 1062 – 1068 (28 October 2004); doi:10.1038/nature02997.
2Christopher Surridge, “Molecular motors: Smooth coupling in Salmonella,” Nature 431, 1047 (28 October 2004); doi:10.1038/4311047b.

The hook region surely appeared to be one of the simplest-looking parts of the complex molecular motor.  Now, even that little item, something that just bends at an angle, is shown to be exquisitely designed, with exacting specifications to allow bending without twisting.  If all the amino acids in this one protein element were not in the right places, the protein would not work.  And if all 120 were not joined together, and were not assembled at the right time and in the right place, the flagellum would be useless.  Inside that hook is an entire highway of molecular trucks that build the propeller (see 06/14/2004 headline).  No wonder Jonathan Wells remarked, “What we find is irreducible complexity all the way down.”

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