Cooperative Ordering of Collagen Triple Helices in the Dense State

• Published in: Langmuir Vol. 23; no. 11; pp. 6411 - 6417
• Main Authors: Gobeaux, F, Belamie, E, Mosser, G, Davidson, P, Panine, P, Giraud-Guille, M.-M
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 22-05-2007
• Subjects: Animals; Anisotropy; Birefringence; Chemistry; Collagen Type I - chemistry; Collagen Type I - ultrastructure; Condensed Matter; Crystallization; Exact sciences and technology; General and physical chemistry; In Vitro Techniques; Microscopy, Electron; Multiprotein Complexes - chemistry; Multiprotein Complexes - ultrastructure; Physics; Protein Conformation; Rats; Scattering, Radiation; Soft Condensed Matter; Thermodynamics; X-Rays; Fluid state; Composition; Organization; Electrostatic interaction; Prediction; Strong interaction; Reflection; Dimension; Small angle X ray scattering; Equilibrium; Phase transitions; Protein; Carboxylic acid; Macromolecule; Order parameter; Collagen; Ordering; Bone; Acetic acid; Structure
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la070093z

Extracellular matrixes such as bone, skin, cornea, and tendon have ordered structures comprised for the most part of collagen, an elongated protein of well-defined dimensions and composition. Here we show how the cooperative ordering of collagen triple helices in the dense fluid state is exploited to produce dense ordered collagen matrixes. The spontaneous formation of a birefringent phase occurs at critical concentrations that increase from 50−60 to 80−85 mg/mL as the acetic acid concentration of the solvent increases from 5 to 500 mM. We studied by small-angle X-ray scattering (SAXS) the local liquidlike positional order across the isotropic/anisotropic phase transition by unwinding the cholesteric phase with moderate shearing stress. Interparticle scattering gives rise to a broad interference peak. The average distance between triple helices, d av, is thus estimated and decreases linearly as a function of φ-1/2 from 12.7 ± 0.9 nm (22.5 mg/mL) to 5.0 ± 0.6 nm (166.4 mg/mL). Equilibrium concentrations and the order parameter of the nematic phase agree reasonably well with theoretical predictions for semiflexible macromolecules. Striated fibrils with a high degree of alignment were obtained by fine-tuning the delicately balanced electrostatic interactions, which yielded strong elastic gels with a hierarchical organization very similar to that of major biological tissues. Typical Bragg reflections corresponding to the 67 nm period characteristic of collagen fibrils in biological tissues were recorded by SAXS with ordered collagen matrixes reconstituted in vitro.