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BP: Fachverband Biologische Physik

BP 32: Posters: Physics of Cells

BP 32.30: Poster

Donnerstag, 25. März 2010, 17:15–20:00, Poster B1

Modelling the Polymorphism of Bacterial Flagella — •Christoph Speier, Reinhard Vogel, and Holger Stark — Institut für Theoretische Physik, TU Berlin

Bacteria such as E.coli propel themselves using a bundle of long helical tails, known as flagella. The main part of the flagellum is a cylindrical structure made from 11 protofilaments that are assembled from thousands of copies of the protein flagellin. This subunit can assume two different states (R and L) with different RR and LL distances. Proteins of the same state are stacked onto each other to form one protofilament. The flagellum can adapt different helical forms (polymorphism). While flagella, in which all proteins are in the same state, form straight tails, they exhibit a helical structure when protofilaments of both R and L type occur. Transitions between different forms of the flagellum can be induced by changing the salt-concentration or the pH value of the solvent and by applying external torques.

The well established Calladine model explains the different possible helical states of the flagellum but provides no understanding why it conventionally assumes the so-called normal state. Refining an existing model, we consider the flagellin protein as a bistable rigid-body unit with state-dependent bonds to neighboring units. Whereas the outer bonds determine the helical form of the filament, the inner bonds are responsible for its structural stability. With our model we can verify that the normal state is only stable when the rigid-body unit assumes an elongated shape in accordance with the real form of flagellin.