Glassy state of native collagen fibril?

Abstract

Our micromechanical experiments show that at physiological temperatures type I collagen fibril has several basic features of the glassy state. The transition out of this state [softening transition] essentially depends on the speed of heating v, e.g., for v = 1 C/min it occurs around 70 C and is displayed by a peak of the internal friction and decreasing Young's modulus. The softening transition decreases by 45 C upon decreasing the heating speed to v = 0.1 C/min. For temperatures 20-30 C the native collagen fibril demonstrates features of mechanical glassines at oscillation frequencies 0.1-3 kHz; in particular, the internal friction has a sharp maximum as a function of the frequency. This is the first example of biopolymer glassines at physiological temperatures, because well-known glassy features of DNA and globular proteins are seen only for much lower temperatures (around 200 K). here-concerning, in particular, the specific role of the hydrated water-the rough physical picture of the glass transition in globular proteins is constructed by an analogy with glass-forming liquids [7,8] and synthetic polymers [9,10]. In particular, it is believed that the largescale conformational motion of proteins freezes at ≈ 200 K, analogously to freezing of cooperative motion in glassforming liquids [7,8] and segmental motion in synthetic polymers [9,10].Thus, the glassy features as such are not important in the native state of globular proteins at physiological temperatures, though the glass transition at much lower temperatures allows to gain some understanding of relevant motions in proteins [7,8].Here we shall demonstrate via micro-mechanical methods that the native type I collagen fibril (made of fibrous protein, type I collagen triple-helices) is in a glassy state at physiological temperatures. This state is displayed via frequency-dependent visco-elastic characteristics (the Young's modulus and the damping decrement) of the native fibril. Upon heating the fibril goes out of the glassy state, a phenomenon known as the softening transition [9,10]. The temperature of this transition depends essentially on the speed of heating, e.g., for the standard heating speed v = 1 C/min it occurs around ≈ 70 C. Note that around 70 C the fibril starts to undergo the denaturation process [13][14][15][16]. This process has been studied by different methods, and some of those methods seems to indicate that this process is inherently irreversible [14]. We saw that upon decreasing the heating speed to v = 0.1 C/min, the softening transition takes place at ≈ 25 C, showing that the glassy features pertain to the native state of the collagen fibril and do not directly relate to its denaturation. We shall also confirm that the glassy features are not seen for the heat-denaturated collagen fibril, and contrast features of the native collagen fibril to those of globular proteins.Type I collagen is the major structural element in the extra-cellular matrix. It forms the basis of fibrous connective tissues, such as tendon, chord, skin, bones, corn...

Physical mechanism for biopolymers to aggregate and maintain in non-equilibrium states

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Thermal-induced force release in oxyhemoglobin

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Eigen Model with Correlated Multiple Mutations and Solution of Error Catastrophe Paradox in the Origin of Life

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