Journal
BIOPHYSICAL JOURNAL
Volume 92, Issue 6, Pages 2230-2236Publisher
BIOPHYSICAL SOCIETY
DOI: 10.1529/biophysj.106.094037
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Funding
- NIAID NIH HHS [AI016478, AI065540, R01 AI065540, R37 AI016478, R01 AI016478, R56 AI065540] Funding Source: Medline
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Bacterial flagella can adopt several different helical shapes in response to varying environmental conditions. A geometric model by Calladine ascribes these discrete shape changes to cooperative transitions between two stable tertiary structures of the constituent protein, flagellin, and predicts an ordered set of 12 helical states called polymorphic forms. Using long polymers of purified flagellin, we demonstrate controlled, reversible transformations between different polymorphic forms. While pulling on a single. lament using an optical tweezer, we record the progressive transformation of the. lament and also measure the force-extension curve. Both normal and coiled polymorphic forms stretch elastically with a bending stiffness of 3.5 pN(.)mu m(2). At a force threshold of 4-7 pN or 3-5 pN ( for normal and coiled forms, respectively), a fraction of the. lament suddenly transforms to the next, longer, polymorphic form. This transformation is not deterministic because the force and amount of transformation vary from pull to pull. In addition, the force is highly dependent on stretching rate, suggesting that polymorphic transformation is associated with an activation energy.
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