Multinuclear magnetic resonance studies of collagen molecular structure and dynamics

Abstract

Abstract We have measured the percentages of cis and trans Gly‐Pro and X‐Hyp peptide bonds in thermally unfolded type I collagen. 13 C‐nmr solution spectra show that 16% of the Gly‐Pro and 8% of the X‐Hyp bonds are cis in unfolded chick calvaria collagen. These results support the hypothesis that cis – trans isomerization is that rate‐limiting step in the propagation of the collagen triple helix. We have used multinuclear solid‐state nmr to study the molecular dynamics of the collagen backbone in tendon, demineralized bone, and intact bone as a function of temperature, hydration, and pH. These studies show that collagen backbone motions are characterized by a broad distribution of correlation times, τ, covering the range from 10 −4 to 10 −9 s. In the case of nonmineralized collagen, the root‐mean‐square fluctuations in azimuthal angle, γ rms , range from ca. 10° when τ ∼ 10 −9 s to ca. 30° when τ < 10 −4 s; in the case of bone collagen, γ rms values are about half as large as those found in nonmineralized collagen. Backbone motions are negligible at temperatures below −25°C. This is also the case at 22°C when demineralized bone collagen is lyophilized. In contrast, flexibility of hydrated demineralized bone collagen greatly increases as pH is lowered from 7 to 2. The more limited flexibility observed at neutral pH is a consequence of the intermolecular interactions that contribute to fibril organization and strength. However, the fibrils retain significant flexibility at physiological pH, enabling them to distribute stress and dissipate mechanical energy.