Sunday, September 14, 2008

Dispatches from the cutting edge of flagellar biology, part 1

Last week I attended the third UK type III secretion meeting, held at the University of Bristol. As with the two previous meetings, it encompassed a wide range of topics within the field of bacterial flagellar biosynthesis and type III secretion. For those of you not familiar with the field, the bacterial flagellum is the chief organelle of motility in bacteria and is related in structure, biosynthesis and evolutionary history to a molecular syringe known as the type III secretion system, which is used by bacteria to inject subversive "effector" proteins into eukaryotic cells. In both cases a complex macromolecular complex is assembled in the cell envelope, with proteins travelling through a central channel that spans two membranes and the periplasm.

The highlight of the meeting were keynote addresses by Keiichi Namba and his colleague Tohru Minamino on the structure and function of the bacterial flagellum. Tohru visited my group a couple of years ago, but I had not met Keiichi before, who has been at the cutting edge of the structural biology of the bacterial flagellum for over a decade. I had a chat with him over lunch. We briefly discussed the silly fuss that the "intelligent design" movement makes over the bacterial flagellum. When I asked him whether they had any problem with creationists in Japan, he just laughed and said, no, that was a problem only in America and Europe.

For more background on this issue, see Ken Miller's The Flagellum Unspun

and this movie of Ken:

and this paper by myself and Nick Matzke.

For me there were two take away messages from Keiichi's talk, one of which I will mention here, the other I will deal with in a subsequent post. Interestingly, Keiichi and colleagues are in the habit of getting superb videos made of their work every year or two, so in each post I will include (a link to) one of Keiichi's videos.

Watch this video from 2004 describing the work of Keiichi's Protonic NanoMachine Project (sorry for the link offsite, have tried and failed to upload it here). Remarkably, by then they had already achieved an atomic resolution structure that effectively spanned the whole flagellar filament (a structure visible by light microscopy!). 

In fact, the filament is part of a series of structures that form the axial components of the bacterial flagellum (filament; hook-filament junction; hook; plus the rod forming the protein export channel in the basal body). In Bristol, Namba reported that he and his colleagues now have structures for all the axial proteins. Interestingly, in every case, the structures show clear homology to one another and to flagellin, confirming earlier suggestions by myself and others that the flagellar axial filament has arisen by a process of successive gene duplications from a single progenitor protein. The way is now open to a detailed reconstruction of the steps leading to the evolution of the axial structures and even to resurrection and investigation of the original axial protein. 

This tremendous pace of advance in the mainstream scientific view of the bacterial flagellum (which accepts evolution as a given)  contrasts markedly with the poverty of the intelligent design viewpoint, which has spawned no new experiments or insights. 

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