Smith J S, Scholtz J M
Department of Medical Biochemistry and Genetics, Texas A&M University, College Station 77843-1114, USA.
Biochemistry. 1996 Jun 4;35(22):7292-7. doi: 10.1021/bi960341i.
To provide a model for understanding the unfolding of proteins by the chemical denaturant guanidine hydrochloride, we have measured helix unfolding for homologous series of peptides with the repeating sequence Ala-Glu-Ala-Ala-Lys-Ala and chain lengths from 7 to 50 residues. The free energy for helix unfolding varies as a function of guanidinium chloride (GdmCl) for all the peptides. The slope of the linear plot of the free energy of helix formation as a function of the molar concentration of GdmCl, termed the m-value, was found to be strongly dependent on the total ionic strength of the solution. A comparison of the m-value for urea denaturation of the same series of peptides [Scholtz, J. M., Barrick, D., York, E. J., Stewart, J. M., & Baldwin, R. L. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 185-189] reveals that, under many conditions, GdmCl is roughly twice as effective as a denaturant than urea on a molar basis, in agreement with many studies on proteins. However, when the ionic strength of aqueous GdmCl is controlled with additional NaCl, it is possible to separate the observed m-value for GdmCl solutions into two components: one that is identical to that found for urea and a second which depends only on the molar concentration of the chloride anion. Therefore, for these peptides, an equimolar mixture of urea and NaCl is nearly as effective as GdmCl in unfolding the helical conformation.
为了提供一个理解化学变性剂盐酸胍使蛋白质解折叠的模型，我们测量了具有重复序列Ala-Glu-Ala-Ala-Lys-Ala且链长从7到50个残基的同源肽系列的螺旋解折叠情况。对于所有这些肽，螺旋解折叠的自由能随盐酸胍（GdmCl）浓度而变化。螺旋形成自由能作为GdmCl摩尔浓度的函数的线性图的斜率，即所谓的m值，被发现强烈依赖于溶液的总离子强度。对同一肽系列尿素变性的m值的比较[Scholtz, J. M., Barrick, D., York, E. J., Stewart, J. M., & Baldwin, R. L. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 185 - 189]表明，在许多情况下，以摩尔计，GdmCl作为变性剂的效力大约是尿素的两倍，这与许多关于蛋白质的研究一致。然而，当用额外的NaCl控制GdmCl水溶液的离子强度时，有可能将观察到的GdmCl溶液的m值分为两个组分：一个与尿素的相同，另一个仅取决于氯离子的摩尔浓度。因此，对于这些肽，尿素和NaCl的等摩尔混合物在使螺旋构象解折叠方面几乎与GdmCl一样有效。
