Yu Y, Monera O D, Hodges R S, Privalov P L
Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA.
J Mol Biol. 1996 Jan 26;255(3):367-72. doi: 10.1006/jmbi.1996.0030.
We have used a synthetic coiled-coil peptide model system to address the long perplexing issue as to why coiled-coils are in general more stable at acidic pH than at neutral pH. Contrary to the above expectation, our results show that at low ionic strength (10 mM) the coiled-coil was much more stable at neutral pH than at acidic pH against both thermal and urea unfolding, indicating that the Lys(+)-Glu- ions pairs present around the coiled-coil interface at neutral pH contribute significantly to the stability of the coiled-coil. However, while the addition of NaCl had no significant effect on the coiled-coil stability at neutral pH, its stability at acidic pH increased dramatically. The cross-over point between the stability at acidic pH and neutral pH occurred at around 100 mM salt, above which the coiled-coil became more stable at acidic pH, in agreement with published results. Therefore, salt effect, rather than intrinsic property, such as carboxyl-carboxyl hydrogen bonding, causes this coiled-coil to become more stable at acidic pH. The preferential stabilizing effect of salt on the coiled-coil at acidic pH can be best explained in terms of the condensation of anions to the positively charged groups on the coiled-coil, the net density of which increases as glutamic acid residues become protonated in acidic pH.
为什么卷曲螺旋通常在酸性pH下比在中性pH下更稳定。与上述预期相反，我们的结果表明，在低离子强度（10 mM）下，卷曲螺旋在中性pH下比在酸性pH下对热和尿素展开更稳定，这表明在中性pH下卷曲螺旋界面周围存在的Lys(+)-Glu-离子对显著有助于卷曲螺旋的稳定性。然而，虽然添加NaCl对中性pH下卷曲螺旋的稳定性没有显著影响，但其在酸性pH下的稳定性却显著增加。酸性pH和中性pH下稳定性的交叉点出现在约100 mM盐浓度处，高于此浓度卷曲螺旋在酸性pH下变得更稳定，这与已发表的结果一致。因此，盐效应而非诸如羧基-羧基氢键等内在性质导致这种卷曲螺旋在酸性pH下更稳定。盐在酸性pH下对卷曲螺旋的优先稳定作用可以最好地用阴离子凝聚到卷曲螺旋上带正电荷的基团来解释，随着谷氨酸残基在酸性pH下质子化，其净密度增加。
