Temperature dependence of H-1 chemical shifts in proteins
Temperature dependence of H-1 chemical shifts in proteins
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DOI：
10.1023/a:1018334207887
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发表时间：
1997-06-01
影响因子：
2.7
通讯作者：
Williamson, MP
中科院分区：
文献类型：
--
作者：
Baxter, NJ;Williamson, MP
用二维核磁共振方法测定了牛胰蛋白酶抑制剂和蛋清溶菌酶两种球状蛋白的酰胺和(CH)- h - α质子化学位移的温度系数。化学位移的温度依赖变化通常是线性的，在全球变性温度以下约15度，推导出的系数范围约为酰胺质子的-16至+2 ppb/K和(CH)- h - α的-4至+3 ppb/K。温度系数可以通过加热引起蛋白质热运动增加的假设来合理化。由于化学位移对原子坐标的微小变化很敏感，从蛋白质坐标推导出的温度系数的精确计算是不可能的。酰胺温度系数与氢键的位置有很好的相关性，这是由晶体学确定的。结论是，温度系数和交换率的结合使用比单独使用两者产生更可靠的氢键指示。如果酰胺质子交换速度慢且温度系数大于-4.5 ppb/K，则为氢键，如果交换速度快且温度系数大于-4.5 ppb/K，则为非氢键。先前观察到的温度系数作为多肽氢键测量的不可靠性可能是由于加热时多肽二级结构的损失。
Temperature coefficients have been measured by 2D NMR methods for the amide and (CH)-H-alpha proton chemical shifts in two globular proteins, bovine pancreatic trypsin inhibitor and hen egg-white lysozyme. The temperature-dependent changes in chemical shift are generally linear up to about 15 degrees below the global denaturation temperature, and the derived coefficients span a range of roughly -16 to +2 ppb/K for amide protons and -4 to +3 ppb/K for (CH)-H-alpha. The temperature coefficients can be rationalized by the assumption that heating causes increases in thermal motion in the protein. Precise calculations of temperature coefficients derived from protein coordinates are not possible, since chemical shifts are sensitive to small changes in atomic coordinates. Amide temperature coefficients correlate well with the location of hydrogen bonds as determined by crystallography. It is concluded that a combined use of both temperature coefficients and exchange rates produces a far more reliable indicator of hydrogen bonding than either alone. If an amide proton exchanges slowly and has a temperature coefficient more positive than -4.5 ppb/K, it is hydrogen bonded, while if it exchanges rapidly and has a temperature coefficient more negative than -4.5 ppb/K, it is not hydrogen bonded. The previously observed unreliability of temperature coefficients as measures of hydrogen bonding in peptides may arise from losses of peptide secondary structure on heating.