Equilibrium thermal transitions of collagen model peptides
Equilibrium thermal transitions of collagen model peptides
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DOI：
10.1110/ps.03501704
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发表时间：
2004-04-01
期刊：
影响因子：
8
通讯作者：
Brodsky, B
中科院分区：
文献类型：
--
作者：
Persikov, AV;Xu, YJ;Brodsky, B
胶原的体外折叠非常缓慢，很难达到平衡，这一特征可能对体内胶原的功能有一定的影响。多肽是研究胶原蛋白三螺旋中平衡热转变的良好模型系统。为了确定一系列不同序列的合成三螺旋多肽是否能够达到平衡，以及三螺旋到未折叠单体的转变是否接近两态模型，进行了研究。如果有足够的时间，所有被研究的多肽的热转变都是完全可逆的。进行了等温实验，得到了不同温度下的松弛时间。在转变初期观察到最慢的松弛时间，约为10-15h，这是由低浓度的自由单体限制的自缔合，而不是顺反异构化的结果。虽然CD平衡转变曲线的拟合和T值与浓度的依赖关系支持双态模型，但将量热焓与范特霍夫热焓进行更严格的比较表明，双态近似并不理想。以往报道的三螺旋主客体多肽的熔融曲线是一个两态的动力学转变，而不是平衡转变。
The folding of collagen in vitro is very slow and presents difficulties in reaching equilibrium, a feature that may have implications for in vivo collagen function. Peptides serve as good model systems for examining equilibrium thermal transitions in the collagen triple helix. Investigations were carried out to ascertain whether a ran-e of synthetic triple-helical peptides of varying sequences can reach equilibrium, and whether the triple helix to unfolded monomer transition approximates a two-state model. The thermal transitions for all peptides studied are fully reversible given sufficient time. Isothermal experiments were carried out to obtain relaxation times at different temperatures. The slowest relaxation times, on the order of 10-15 h, were observed at the beginning of transitions, and were shown to result from self-association limited by the low concentration of free monomers, rather than cis-trans isomerization. Although the fit of the CD equilibrium transition curves and the concentration dependence of T values support a two-state model, the more rigorous comparison of the calorimetric enthalpy to the van't Hoff enthalpy indicates the two-state approximation is not ideal. Previous reports of melting curves of triple-helical host-guest peptides are shown to be a two-state kinetic transition, rather than an equilibrium transition.