Moriyama Yoshiko, Takeda Kunio
Department of Applied Chemistry and Biotechnology, Okayama University of Science.
J Oleo Sci. 2017 May 1;66(5):521-529. doi: 10.5650/jos.ess16228. Epub 2017 Apr 13.
The secondary structural changes of human serum albumin with the intact 17 disulfide bridges (HSA) and the disulfide bridges-cleaved human serum albumin (RCM-HSA) in thermal denaturation were examined. Most of the helical structures of HSA, whose original helicity was 66%, were sharply disrupted between 50 and 100°C. However, 14% helicity remained even at 130°C. The temperature dependence of the degree of disrupted helical structures of HSA was discussed in connection with questions about a general protein denaturation model. When HSA lost the disulfide bridges, about two-thirds of the original helices were disrupted. Although the helices of RCM-HSA remaining after the cleavage of the disulfide bridges were relatively resistant against the heat treatment, the helicity changed from 22% at 25°C to 14% at 130℃. The helicity of RCM-HSA at 130°C agreed with the helicity of HSA at the same temperature, indicating that the same helical moieties of the polypeptides remained unaffected at this high temperature. The additive effects of sodium dodecyl sulfate (SDS) on the structural changes of HSA and RCM-HSA in thermal denaturation were also examined. A slight amount of SDS protected the helical structures of HSA from thermal denaturation below 80°C. Upon cooling to 25°C after heat treatment at temperatures below 70°C with the coexistence of SDS of low concentrations, the helical structures of HSA were reformed to the original level at 25°C before heating. A similar tendency was also observed after heat treatment at 80°C. In contrast, the helical structures of the RCM-HSA complexes with SDS are completely recovered upon cooling to 25°C even after heat treatment up to 100°C. Similar investigations were also carried out on bovine serum albumins which had the intact 17 disulfide bridges and lost all of the bridges.
研究了具有完整17个二硫键的人血清白蛋白（HSA）和二硫键断裂的人血清白蛋白（RCM-HSA）在热变性过程中的二级结构变化。HSA的大部分螺旋结构（其原始螺旋度为66%）在50至100°C之间急剧破坏。然而，即使在130°C时仍保留14%的螺旋度。结合一般蛋白质变性模型的问题，讨论了HSA螺旋结构破坏程度的温度依赖性。当HSA失去二硫键时，约三分之二的原始螺旋被破坏。虽然二硫键断裂后剩余的RCM-HSA的螺旋对热处理相对抗性，但螺旋度从25°C时的22%变为130°C时的14%。130°C时RCM-HSA的螺旋度与相同温度下HSA的螺旋度一致，表明多肽的相同螺旋部分在该高温下未受影响。还研究了十二烷基硫酸钠（SDS）对HSA和RCM-HSA热变性结构变化的加和效应。少量SDS在80°C以下保护HSA的螺旋结构免受热变性。在低于70°C的温度下与低浓度SDS共存进行热处理后冷却至25°C时，HSA的螺旋结构恢复到加热前25°C时的原始水平。在80°C热处理后也观察到类似趋势。相反，即使在高达100°C的热处理后，RCM-HSA与SDS复合物的螺旋结构在冷却至25°C时也能完全恢复。对具有完整17个二硫键和失去所有二硫键的牛血清白蛋白也进行了类似研究。
