Probing the Physical Determinants of Thermal Expansion of Folded Proteins
Probing the Physical Determinants of Thermal Expansion of Folded Proteins
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DOI：
10.1021/jp401113p
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发表时间：
2013-10-24
影响因子：
3.3
通讯作者：
Royer, Catherine A.
中科院分区：
文献类型：
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作者：
Dellarole, Mariano;Kobayashi, Kei;Royer, Catherine A.
蛋白质展开时体积变化的大小和符号强烈依赖于温度。这种温度依赖关系反映了折叠和展开状态的热膨胀率的差异。决定蛋白质摩尔膨胀率的因素以及相似摩尔体积的蛋白质在热膨胀率上的巨大差异还不是很清楚。模型化合物研究表明，水分子在加热时从蛋白质表面转移到本体的摩尔体积的差异是主要贡献。加热时内部不含溶剂的空隙的膨胀是另一个可能的因素。在这里，水化密度对蛋白质摩尔热膨胀性的贡献是通过比较牛胰蛋白酶抑制剂及其变异体和蛋白质水界面上或附近的丙氨酸取代物来检验的。这些蛋白质中的两个的变种，加上一个额外的突变，可以在自然条件下展开，也被研究了。与亲本蛋白质相比，丙氨酸变体在折叠和未折叠状态下的热膨胀性都略有下降，这表明蛋白质的外部极性可以做出很大的改变，而不会导致随后的热膨胀性的大变化。考虑到丙氨酸残基的摩尔体积很小，这种温和的影响并不令人惊讶。通过测量一种高度稳定的葡萄球菌核酸酶的含腔变体的热膨胀来探讨内部空腔体积的膨胀的贡献。与参考蛋白质相比，这些含有空洞的蛋白质的摩尔膨胀系数明显更大(2-3倍)。综上所述，这些结果表明，折叠蛋白质热膨胀性的一个关键决定因素在于内部排除溶剂的空隙的膨胀。
The magnitude and sign of the volume change upon protein unfolding are strongly dependent on temperature. This temperature dependence reflects differences in the thermal expansivity of the folded and unfolded states. The factors that determine protein molar expansivities and the large differences in thermal expansivity for proteins of similar molar volume are not well understood. Model compound studies have suggested that a major contribution is made by differences in the molar volume of water molecules as they transfer from the protein surface to the bulk upon heating. The expansion of internal solvent-excluded voids upon heating is another possible contributing factor. Here, the contribution from hydration density to the molar thermal expansivity of a protein was examined by comparing bovine pancreatic trypsin inhibitor and variants with alanine substitutions at or near the protein water interface. Variants of two of these proteins with an additional mutation that unfolded them under native conditions were also examined. A modest decrease in thermal expansivity was observed in both the folded and unfolded states for the alanine variants compared with the parent protein, revealing that large changes can be made to the external polarity of a protein without causing large ensuing changes in thermal expansivity. This modest effect is not surprising, given the small molar volume of the alanine residue. Contributions of the expansion of the internal void volume were probed by measuring the thermal expansion for cavity-containing variants of a highly stable form of staphylococcal nuclease. Significantly larger (2-3-fold) molar expansivities were found for these cavity-containing proteins relative to the reference protein. Taken together, these results suggest that a key determinant of the thermal expansivities of folded proteins lies in the expansion of internal solvent-excluded voids.