Zernia Göran, Huster Daniel
Junior Research Group Solid-State NMR Studies of the Structure of Membrane-Associated Proteins, University of Leipzig, D-04107 Leipzig, Germany.
NMR Biomed. 2006 Dec;19(8):1010-9. doi: 10.1002/nbm.1061.
Cartilage is a complex biological tissue consisting of collagen, proteoglycans and water. The structure and molecular mobility of the collagen component of cartilage were studied by (13)C solid-state NMR spectroscopy as a function of hydration. The hydration level of cartilage was adjusted between fully hydrated ( approximately 80 wt% H(2)O) and highly dehydrated ( approximately 30 wt% H(2)O) using the osmotic stress technique. Thus, the conditions of mechanical load could be simulated and the response of the tissue macromolecules to mechanical stress is reported. From the NMR measurements, the following results were obtained. (i) Measurements of motionally averaged dipolar (1)H-(13)C couplings were carried out to study the segmental mobility in cartilage collagen at full hydration. Backbone segments undergo fast motions with amplitudes of approximately 35 degrees whereas the collagen side-chains are somewhat more mobile with amplitudes between 40 and 50 degrees . In spite of the high water content of cartilage, collagen remains essentially rigid. (ii) No chemical shift changes were observed in (13)C cross-polarization magic angle spinning spectra of cartilage tissue at varying hydration indicating that the collagen structure was not altered by application of high osmotic stress. (iii) The (1)H-(13)C dipolar coupling values detected for collagen signals respond to dehydration. The dipolar coupling values gradually increase upon cartilage dehydration, reaching rigid limit values at approximately 30 wt% H(2)O. This indicates that collagen is essentially dehydrated in cartilage tissue under very high mechanical load, which provides insights into the elastic properties of cartilage collagen, although the mechanical pressures applied here exceed the physiological limit.
软骨是一种由胶原蛋白、蛋白聚糖和水组成的复杂生物组织。利用¹³C固态核磁共振光谱研究了软骨胶原蛋白成分的结构和分子流动性与水合作用的关系。采用渗透应力技术将软骨的水合水平在完全水合（约80 wt% H₂O）和高度脱水（约30 wt% H₂O）之间进行调节。由此可以模拟机械负荷条件，并报告组织大分子对机械应力的响应。通过核磁共振测量得到了以下结果。（i）进行了运动平均偶极¹H-¹³C耦合测量，以研究完全水合状态下软骨胶原蛋白的片段流动性。主链片段经历快速运动，振幅约为35度，而胶原蛋白侧链的流动性稍大，振幅在40至50度之间。尽管软骨含水量高，但胶原蛋白基本上保持刚性。（ii）在不同水合状态下的软骨组织¹³C交叉极化魔角旋转光谱中未观察到化学位移变化，这表明高渗透应力的施加并未改变胶原蛋白的结构。（iii）检测到的胶原蛋白信号的¹H-¹³C偶极耦合值对脱水有响应。随着软骨脱水，偶极耦合值逐渐增加，在约30 wt% H₂O时达到刚性极限值。这表明在非常高的机械负荷下，软骨组织中的胶原蛋白基本上是脱水的，这为软骨胶原蛋白的弹性特性提供了见解，尽管这里施加的机械压力超过了生理极限。
