title: Mechanical transition from α-helical coiled coils to β-sheets in fibrin(ogen).
abstract: 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.
authors.affiliation: Department of Chemistry, University of Massachusetts, Lowell, Massachusetts 01854, United States.
authors.forename: Artem
authors.initials: A
authors.lastname: Zhmurov
authors.forename: Olga
authors.initials: O
authors.lastname: Kononova
authors.forename: Rustem I
authors.initials: RI
authors.lastname: Litvinov
authors.forename: Ruxandra I
authors.initials: RI
authors.lastname: Dima
authors.forename: Valeri
authors.initials: V
authors.lastname: Barsegov
authors.forename: John W
authors.initials: JW
authors.lastname: Weisel
mesh_terms: D005337:Fibrin / Q000737:chemistry*; D005340:Fibrinogen / Q000737:chemistry*; D008958:Models, Molecular; D011487:Protein Conformation; D011489:Protein Denaturation
chemical_list: D005337:Fibrin; D005340:Fibrinogen