The α-Helix to β-Sheet Transition in Stretched and Compressed Hydrated Fibrin Clots

Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
Biophysical Journal (Impact Factor: 3.97). 09/2012; 103(5):1020-7. DOI: 10.1016/j.bpj.2012.07.046
Source: PubMed


Fibrin is a protein polymer that forms the viscoelastic scaffold of blood clots and thrombi. Despite the critical importance of fibrin deformability for outcomes of bleeding and thrombosis, the structural origins of the clot's elasticity and plasticity remain largely unknown. However, there is substantial evidence that unfolding of fibrin is an important part of the mechanism. We used Fourier transform infrared spectroscopy to reveal force-induced changes in the secondary structure of hydrated fibrin clots made of human blood plasma in vitro. When extended or compressed, fibrin showed a shift of absorbance intensity mainly in the amide I band (1600-1700 cm(-1)) as well as in the amide II and III bands, indicating an increase of the β-sheets and a corresponding reduction of the α-helices. The structural conversions correlated directly with the strain or pressure and were partially reversible at the conditions applied. The additional absorbance observed at 1612-1624 cm(-1) was characteristic of the nascent interchain β-sheets, consistent with protein aggregation and fiber bundling during clot deformation observed using scanning electron microscopy. We conclude that under extension and/or compression an α-helix to β-sheet conversion of the coiled-coils occurs in the fibrin clot as a part of forced protein unfolding.

Download full-text


Available from: Rustem I Litvinov, Jul 06, 2015
  • Source
    • "Fourier transform infrared spectroscopy in the attenuated total reflectance mode (FTIR-ATR, Equimo55 bruker FTIR spectrometer) was used to examine the SF structural changes during electrospinning in methanol coagulation bath. The quantitative analysis of amide I absorption band within the 1600–1700 cm À 1 region [16] [17], was done using curve-fitting and de-convolution methods to determine the amount of α-helix, β-sheet, and random coil elements in each spectrum. 2.3. "
    [Show abstract] [Hide abstract]
    ABSTRACT: New bioactive nanobiocomposite scaffolds based on silk fibroin nanofiber-porous starch are presented for potential bone tissue regeneration. The silk fibroin nanofibers were fabricated directly via wet electrospinning using methanol coagulation bath and then the chopped electrospun nanofibers were incorporated into the starch matrix, followed by particulate leaching and freeze-drying. To achieve bioactivity, the calcium phosphate was then deposited throughout the fabricated scaffolds via alternate soaking in saturated calcium and phosphate solutions at 37 °C. The morphology, structure, swelling, and calcium phosphate forming ability of the scaffolds were evaluated and the results indicated that addition of silk fibroin nanofibers into the starch matrix reduced the mean pore size, porosity, and water uptake of the fabricated scaffolds. Moreover, the deposited calcium phosphate layer consists of both brushite and apatitic calcium phosphate. The highest amount of formed calcium phosphate is evident in the starch matrix and increasing the amount of silk fibroin nanofibers decreases calcium phosphate formation. Cell culture experiments with osteoblast-like cells (MG63) on the scaffolds coated with calcium phosphate demonstrated that incorporation of SF nanofibers into the starch hydrogel improves cell viability, proliferation, and attachment.
    Full-text · Article · May 2015 · Ceramics International
  • Source
    [Show abstract] [Hide abstract]
    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.
    Full-text · Article · Sep 2012 · Journal of the American Chemical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Fibrin fibers form the structural scaffold of blood clots. Thus, their mechanical properties are of central importance to understanding hemostasis and thrombotic disease. Recent studies have revealed that fibrin fibers are elastomeric despite their high degree of molecular ordering. These results have inspired a variety of molecular models for fibrin's elasticity, ranging from reversible protein unfolding to rubber-like elasticity. An important property that has not been explored is the timescale of elastic recoil, a parameter that is critical for fibrin's mechanical function and places a temporal constraint on molecular models of fiber elasticity. Using high-frame-rate imaging and atomic force microscopy-based nanomanipulation, we measured the recoil dynamics of individual fibrin fibers and found that the recoil was orders of magnitude faster than anticipated from models involving protein refolding. We also performed steered discrete molecular-dynamics simulations to investigate the molecular origins of the observed recoil. Our results point to the unstructured αC regions of the otherwise structured fibrin molecule as being responsible for the elastic recoil of the fibers.
    Full-text · Article · Jun 2013 · Biophysical Journal
Show more