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Protein-Protein Interactions in Single Bacteria Flagella

Protein-Protein Interactions in Single Bacteria Flagella. Aryeh Warmflash Advisor Prof. Norbert Scherer, Department of Chemistry. Purpose. To gain a better understanding of protein-protein interactions in general by exploring the mechanics of flagella

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Protein-Protein Interactions in Single Bacteria Flagella

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  1. Protein-Protein Interactions in Single Bacteria Flagella Aryeh Warmflash Advisor Prof. Norbert Scherer, Department of Chemistry

  2. Purpose • To gain a better understanding of protein-protein interactions in general by exploring the mechanics of flagella • Protein-protein interactions are crucial to innumerable processes in biology • There is abundant biochemical and structural data on flagella making them ideal for study. However, how the structure facilitates the function of flagella is unclear. • Studying the mechanics of flagella will help answer this question.

  3. Background Information • Bacteria are propelled by tail-like appendages called flagella • Flagella are composed of protein subunits called flagellin and have a helical structure which changes handedness when the direction of rotation is reversed. • Normal flagella are left-handed and can transition to right-handedness. Right handed (unable to transition) and straight mutants are also studied. • The flagella are modeled as having two separate interactions- soft, axial and rigid, lateral interactions • The interplay between these is used to explain the ability of the flagella to change states while maintaining its overall structure.

  4. The Model • In the stretched state, the behavior is elastic. We model force v. extension as: F~k/(1-l /L) where L is fixed contour length of the helix and k is the intrinsic rigidity • In the over-stretched state (when helix is >80% extended) a rigid linear term is added:F~k/(1-l /L) + K(l /L-1) • Boltzmann statistics with an external force f then gives the extension, l .

  5. Method • Flagella are covalently bonded to an Atomic Force Microscope (AFM) Cantilever which is used to apply a force • Cantilever pulls with constant velocity. Force and extension are measured • Range is approximately 10 pN to 1 nN

  6. Project Part I --Hysteresis • Hysteresis has been observed in the pulling and retracting of flagella • Hysteresis is related to the energy barrier between the packed and unpacked states and the repacking rate • In the first part of my project, I will quantify the dependence of the hysteresis on the rate of pulling

  7. Project Part II – Constant Force Measurement • All past measurements have been done at constant velocity and have measured force and extension. • Part II of the project will be to design hardware which will make the AFM cantilever pull with constant force. • With the AFM in constant force mode, we can measure the time intervals between breakage events as a function of the applied force. • This data can be used to compute a free energy curve • This will also connect to the research on hysteresis. The hysteresis can be used to determine the irreversible work. Using Jarzynski’s equality, this can also be used to compute the free energy.

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