Investigation of the Stabilizing Mechanism of Collagen

已知Hyp^R残基有助于胶原蛋白三螺旋结构的热稳定性。我们进行了深入的研究，从热力学的角度研究了一系列多肽（X-Y- gly）_n [X, Y: Pro, Hyp^R，或4-氟脯氨酸（fPro）]对胶原三螺旋结构的稳定机制。DSC分析所得的三螺旋结构向单螺旋结构转变的热力学参数表明，（Pro-Hyp^R-Gly）_<10>的稳定性增强主要由焓项引起，而（Pro-fPro^R-Gly）_<10>和（fPro^s-Pro-Gly）_<10>的稳定性增强主要由熵项引起。我们通过比较溶液中观察到的分子体积和晶体结构中的固有分子体积，证明了这种差异来自于这些肽的水合作用的差异。另一方面，X位的Hyp^R残基降低了三螺旋结构的稳定性。为了解决Hyp^R的这种影响，我们合成并表征了（Hyp^R-Hyp^R- gly）_<10>。我们已经报道了它需要一个热稳定的三螺旋结构，但是，它的稳定机制还没有解决。我们测定了（Hyp^R-Hyp^R-Gly）_<10>的全长晶体结构。为了证实这一精确的结构信息，我们估计了三螺旋和单螺旋状态下的水化程度。结果表明，（Hyp^R-Hyp^R-Gly）_<10>的水化程度与（Pro-Hyp^R-Gly）_<10>在三螺旋状态下相当，但前者的水化程度高于（Pro-Hyp^R-Gly）_<10>在单螺旋状态下。由于水合作用降低了与水分子形成氢键的焓，同时由于水分子在肽分子周围的限制而降低了熵，我们推断（Hyp^R-Hyp^R-Gly）_<10>的高热稳定性归因于其在单圈状态下的高度水合作用。少

It has been known that Hyp^R residue contributes to the thermal stability of the collagen triple helical structure. We have performed intensive studies to investigate the stabilizing mechanism of the collagen triple helical structure using a series of polytripeptides (X-Y-Gly)_n [X, Y : Pro, Hyp^R, or 4-fluoroproline (fPro)] from the thermodynamic point of view. The thermodynamic parameters with the transition from the triple-helix to the single-coil determined by DSC analyses indicated that the enhanced stabilities are classified into two different types : the enthalpy term is primarily responsible for increased stability of (Pro-Hyp^R-Gly)_<10>, whereas the entropy term dominates the enhanced stabilities of (Pro-fPro^R-Gly)_<10> and (fPro^s-Pro-Gly)_<10>. We showed that this difference comes from the difference of hydration on these peptides by the comparison of molecular volumes observed in solution with intrinsic ones from the crystal structure.On the other hand, it has been shown … More that Hyp^R residue at the X position decreases the stability of the triple helix. To address this effect of Hyp^R, we have synthesized and characterized (Hyp^R-Hyp^R-Gly)_<10>. We have already reported that it takes a thermally stable triple helix, however, its stabilizing mechanism has not been solved. Here we determined the full-length crystal structure of (Hyp^R-Hyp^R-Gly)_<10>. To corroborate this precise structural information, we estimated the degrees of hydration in both the triple-helix and the single-coil states. The results showed that the degree of hydration of (Hyp^R-Hyp^R-Gly)_<10> is comparable to that of (Pro-Hyp^R-Gly)_<10> in the triple-helix state, but the former was more highly hydrated than (Pro-Hyp^R-Gly)_<10> in the single-coil state. Because hydration reduces the enthalpy due to the formation of hydrogen bond with water molecule and diminishes the entropy due to the restriction of water molecules surrounding a peptide molecule, we deduced that the high thermal stability of (Hyp^R-Hyp^R-Gly)_<10> is attributed to its high degree of hydration in the single-coil state. Less