Key Laboratory of Leather Chemistry and Engineering of Ministry of Education, National Engineering Laboratory for Clean Technology of Leather Manufacture, School of Chemical Engineering, Sichuan University, Chengdu, Sichuan, China.
J Inorg Biochem. 2012 Dec;117:124-30. doi: 10.1016/j.jinorgbio.2012.08.017. Epub 2012 Sep 1.
Ultrasensitive differential scanning calorimetry (US-DSC) was used to directly measure the thermal transition temperature and energy change of acid soluble collagen in the presence of Cr(3+) and Al(3+) sulfates. The behavior of Cr(3+) was analogous to kosmotropes in the cation Hofmeister series and increased the stability of collagen in dilute solutions. Meanwhile, the denaturational enthalpy change (ΔH) of collagen was substantially reduced with change to increasing Cr(3+) concentration. This is likely due to the uni-point binding of Cr(3+) with carboxyl groups of collagen side chains that could decrease the hydrogen-bonding in collagen and result in the increase of protein hydrophobicity. In the case of Al(3+), the interactions between the ions and collagen showed very different properties: at low and medium ion concentrations, the stability of the collagen was decreased; however, a further increase of Al(3+) concentration led to a salting-out effect of collagen, indicating the Al(3+) is a typical chaotropic ion. This striking difference of the two ions in the stabilization of collagen can be explained in terms of the different interactions between the cations and the carboxyl groups of collagen side chains. Additionally, we studied metal ion induced conformational change by the combination of circular dichroism (CD) and atomic force microscopy (AFM). CD measurements revealed that neither metal ion interactions of collagen with Cr(3+) nor Al(3+) ions destroyed the triple-helical backbone structure of collagen in the solution. AFM results further confirmed that the dehydration of collagen by Cr(3+) is more significant than Al(3+), thus inducing the aggregation of collagen fibrils.
超灵敏差示扫描量热法（US-DSC）被用于直接测量在 Cr(3+) 和 Al(3+) 硫酸盐存在下酸溶性胶原蛋白的热转变温度和能量变化。Cr(3+) 的行为类似于阳离子 Hofmeister 序列中的亲水分子，增加了胶原蛋白在稀溶液中的稳定性。同时，随着 Cr(3+)浓度的增加，胶原蛋白的变性焓变（ΔH）显著降低。这可能是由于 Cr(3+)与胶原蛋白侧链羧基的单点结合，降低了胶原蛋白中的氢键，导致蛋白质疏水性增加。对于 Al(3+)，离子与胶原蛋白之间的相互作用表现出非常不同的性质：在低浓度和中浓度离子下，胶原蛋白的稳定性降低；然而，进一步增加 Al(3+)浓度会导致胶原蛋白的盐析效应，表明 Al(3+)是一种典型的离液离子。这两种离子在稳定胶原蛋白方面的显著差异，可以用阳离子与胶原蛋白侧链羧基之间的不同相互作用来解释。此外，我们还通过圆二色性（CD）和原子力显微镜（AFM）的结合研究了金属离子诱导的构象变化。CD 测量表明，Cr(3+)与胶原蛋白的金属离子相互作用以及 Al(3+)离子都没有破坏胶原蛋白在溶液中的三螺旋骨架结构。AFM 结果进一步证实，Cr(3+)对胶原蛋白的脱水作用比 Al(3+)更明显，从而导致胶原蛋白纤维的聚集。
