Phase transition from α-helices to β-sheets in supercoils of fibrillar proteins

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The transition from α-helices to β-strands under external mechanical force in fibrin molecule containing coiled-coils is studied and free energy landscape is resolved. The detailed theoretical modeling of each stage of coiled-coils fragment pulling process was performed. The plots of force (F) as a function of molecule expansion (X) for two symmetrical fibrin coiled-coils (each ∼17 nm in length) show three distinct modes of mechanical behaviour: (1) linear (elastic) mode when coiled-coils behave like entropic springs (F<100−125 pN and X<7−8 nm), (2) viscous (plastic) mode when molecule resistance force does not increase with increase in elongation length (F≈150 pN and X≈10−35 nm) and (3) nonlinear mode (F>175−200 pN and X>40−50 nm). In linear mode the coiled-coils unwind at 2π radian angle, but no structural transition occurs. Viscous mode is characterized by the phase transition from the triple α-spirals to three-stranded parallel β-sheet. The critical tension of α-helices is 0.25 nm per turn, and the characteristic energy change is equal to 4.9 kcal/mol. Changes in internal energy Δu, entropy Δs and force capacity cf per one helical turn for phase transition were also computed. The observed dynamic behavior of α-helices and phase transition from α-helices to β-sheets under tension might represent a universal mechanism of regulation of fibrillar protein structures subject to mechanical stresses due to biological forces.

Keywords: phase transition from α-helices to β-sheets, thermodynamics of transition from α-helices to β-sheets, molecular modeling, fibrinogen, fibrin fibers, Molecular Dynamics, GPU
Citation in English: Zhmurov A.A., Alekseenko A.E., Barsegov V.A., Kononova O.G., Kholodov Y.A. Phase transition from α-helices to β-sheets in supercoils of fibrillar proteins // Computer Research and Modeling, 2013, vol. 5, no. 4, pp. 705-725
Citation in English: Zhmurov A.A., Alekseenko A.E., Barsegov V.A., Kononova O.G., Kholodov Y.A. Phase transition from α-helices to β-sheets in supercoils of fibrillar proteins // Computer Research and Modeling, 2013, vol. 5, no. 4, pp. 705-725
DOI: 10.20537/2076-7633-2013-5-4-705-725
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