Wrabl J, Holtzer M E, Holtzer A
Department of Chemistry, Washington University, St. Louis, Missouri 63130.
Biopolymers. 1994 Dec;34(12):1659-67. doi: 10.1002/bip.360341210.
CD studies are presented on thermal unfolding of coiled-coil homodimers of two genetic variant chains of chicken gizzard tropomyosin (CG-Tm). The experiments include the effects of cross-linking both isoforms and the dependence on protein concentration of unfolding in both reduced isoforms, variables not examined in extant work. The general shapes of the unfolding curves for singly cross-linked species depend on whether the cross-link is at C190 (its site on one isoform) or at C36 (its site on the other). These curves are compared with extant ones for various cross-linked species of rabbit tropomyosin. The comparison supports the view that the unfolding behavior of cross-linked species results from a complex interaction of strain at the cross-link, local variations in structural stability, and loop entropy. The observed concentration dependence of the transition temperature for the uncross-linked (reduced) species of CG-Tm is very small (2.9 degrees C) for one variant homodimer and unobservably small (< 2 degrees C) for the other in the 100-fold concentration range (approximately 0.01-1.0 mg/mL) accessible here. These experimental values of delta Tm are much smaller than are predicted from extant values of the van't Hoff transition enthalpies, calling the latter into question.
本文展示了关于鸡胃原肌球蛋白（CG-Tm）两条基因变异链的卷曲螺旋同型二聚体热解折叠的圆二色性（CD）研究。实验包括交联两种异构体的影响以及两种还原异构体解折叠对蛋白质浓度的依赖性，这些变量在现有研究中未被考察。单交联物种解折叠曲线的总体形状取决于交联是在C190（一种异构体上的位点）还是在C36（另一种异构体上的位点）。将这些曲线与兔原肌球蛋白各种交联物种的现有曲线进行比较。该比较支持以下观点：交联物种的解折叠行为是由交联处的应变、结构稳定性的局部变化和环熵的复杂相互作用导致的。在此可达到的100倍浓度范围（约0.01 - 1.0 mg/mL）内，对于一种变异同型二聚体，CG-Tm未交联（还原）物种的转变温度的观测浓度依赖性非常小（2.9摄氏度），而对于另一种则小到无法观测（< 2摄氏度）。这些ΔTm的实验值远小于根据现有范特霍夫转变焓值预测的值，这使得后者受到质疑。
