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SUMMARY:Bacterial flagellar filaments: smart structure\, smart protein - P
 rofessor Chris Calladine\, Emeritus Professor CUED
DTSTART:20110128T143000Z
DTEND:20110128T153000Z
UID:TALK29050@talks.cam.ac.uk
CONTACT:Ms Helen Gardner
DESCRIPTION:Bacterial flagellar filaments are the corkscrew-like propeller
 s that enable bacteria such as Salmonella to swim in their aqueous environ
 ment.  A flagellar filament is built\, typically\, from about 30\,000 iden
 tical molecules of the protein flagellin.  It has left-handed helical twis
 t for normal swimming\; but it transforms to a right-handed corkscrew when
  driven in reverse by its rotary motor during the “tumbling” manoever 
 of chemotaxis.\n\nAny helical form here is an engineering paradox: for if 
 the building-blocks were in identical environments with respect to their n
 eighbours\, the filaments would have to be straight.\n\nIn the 1970s it wa
 s shown that\, in different circumstances\, flagellar filaments can adopt 
 a range of different helical wave-forms\, depending e.g. on mechanical tor
 que (as above)\; pH of the environment\; or single amino-acid mutations of
  the flagellin protein.  But all of these different wave-forms were member
 s of a single family of discrete forms – which included two extreme\, st
 raight varieties having Left- and Right-handed twist\, respectively.  In p
 rinciple\, this family could be explained by a quasi-mechanical conformati
 onal “switch” somewhere within the flagellin building-block.\n\nIn thi
 s talk I shall discuss two recent (2003\, 2010) studies by Namba and colle
 agues\, by means of cryo-electron-microscopy\, of the L and R straight fil
 aments of Salmonella at 4 Ǻ resolution.  I shall use the difference betwe
 en these two structures to elucidate not only the switching mechanism\, bu
 t also the way in which a given flagellin mutant can determine which membe
 r of the family of discrete forms is to be constructed.\n\nIn building the
 se helical flagellar filaments\, nature makes use of helical structures at
  four different levels.
LOCATION:Department of Engineering - LR6
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