Mechanical transition from α-helical coiled coils to β-sheets in fibrin(ogen)

J Am Chem Soc. 2012 Dec 19;134(50):20396-402. doi: 10.1021/ja3076428. Epub 2012 Sep 25.


We characterized the α-to-β transition in α-helical coiled-coil connectors of the human fibrin(ogen) molecule using biomolecular simulations of their forced elongation and theoretical modeling. The force (F)-extension (X) profiles show three distinct regimes: (1) the elastic regime, in which the coiled coils act as entropic springs (F < 100-125 pN; X < 7-8 nm); (2) the constant-force plastic regime, characterized by a force-plateau (F ≈ 150 pN; X ≈ 10-35 nm); and (3) the nonlinear regime (F > 175-200 pN; X > 40-50 nm). In the plastic regime, the three-stranded α-helices undergo a noncooperative phase transition to form parallel three-stranded β-sheets. The critical extension of the α-helices is 0.25 nm, and the energy difference between the α-helices and β-sheets is 4.9 kcal/mol per helical pitch. The soft α-to-β phase transition in coiled coils might be a universal mechanism underlying mechanical properties of filamentous α-helical proteins.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Fibrin / chemistry*
  • Fibrinogen / chemistry*
  • Models, Molecular
  • Protein Conformation
  • Protein Denaturation


  • Fibrin
  • Fibrinogen