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A study of metaquomyoglobin in solution by NMR spectroscopy. Structural properties and histidine ionization

机译：核磁共振波谱法研究溶液中的变质肌红蛋白。结构性质和组氨酸电离

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摘要

One- and two-dimensional proton NMR spectroscopy was employed to characterize the solution structure of sperm whale metaquomyoglobin and the ionization properties of its histidine residues: structural information was obtained through analysis of paramagnetic dipolar shifts and p$Ksb{rm a}$ values were determined with titration experiments under various salt conditions.;The dipolar contribution to the paramagnetic shift was estimated by taking the difference between the chemical shifts in metaquomyoglobin (S = 5/2) and carbonmonoxymyoglobin (S = 0). This contribution is directly proportional to the geometric factor and the zero-field splitting constant (D), which was determined to be 9.66 $pm$ 0.08 cm$sp{-1}$ in a self-consistent manner. The observed dipolar shifts were compared to the values calculated with the X-ray coordinates and D. There is good agreement between calculated and observed dipolar shifts in nearly 80% of the cases. Thus, the X-ray structure is similar to the solution structure and the dipolar shift can be used to confirm spectral assignments. Discrepancies were noted in the A-G-H and G-H interfaces and in turns. For several regions, the deviations could be rationalized with features specific to the metaquomyoglobin solid state structure.;Unambiguous spectral assignment and p$Ksb{rm a}$s were obtained for all histidine resonances, except those in contact with the heme group, His-64, -93 and -97. His-12, -81, and -116 have p$Ksb{rm a}rm s$ close to that of an exposed histidine (6.6). His-48 and -113 have depressed p$Ksb{rm a}$s indicating a local environment that favors the neutral state. His-36 has a high p$Ksb{rm a}$ ($>$7.5), which implies strong interactions with negative charge(s). His-24 and 82 are buried in the neutral state even at low pH. His-119 has a relatively normal p$Ksb{rm a}$, but a hydrogen bond with His-24 increases the complexity of the ionization process. The titrations of His-12 and His-48 cannot be explained by X-ray structure. The p$Ksb{rm a}$ of His-113 has the strongest dependence on the salt concentration (0.2 M and 1.5 M NaCl). Changing the salt concentration does not affect significantly the p$Ksb{rm a}$ of His-36, and -48. The p$Ksb{rm a}$ of other histidines increases slightly with salt concentration, indicating a simple ionic shielding effect. Similar data were collected on horse metaquomyoglobin.
机译：使用一维和二维质子NMR光谱来表征抹香鲸变红血红蛋白的溶液结构及其组氨酸残基的电离特性：通过分析顺磁偶极位移获得结构信息，p $ Ksb {rm a} $的值分别为通过在各种盐条件下的滴定实验确定;偶极对顺磁位移的贡献是通过计算变质肌红蛋白（S = 5/2）和一氧化碳肌红蛋白（S = 0）的化学位移之间的差来估算的。该贡献与几何因子和零场分裂常数（D）成正比，该常数以自洽方式确定为9.66 $ pm $ 0.08 cm $ sp {-1} $。将观察到的偶极位移与通过X射线坐标和D计算的值进行比较。在近80％的情况下，计算出的偶极位移与观察到的偶极位移之间有很好的一致性。因此，X射线结构类似于溶液结构，并且偶极位移可用于确认光谱分配。依次在A-G-H和G-H接口中发现了差异。对于几个区域，可以用特变肌红蛋白固态结构特有的特征合理化偏差。除与血红素组His接触的组氨酸共振外，所有组氨酸共振均获得明确的光谱分配和p $ Ksb {rm a} $ s。 -64，-93和-97。 His-12，-81和-116的p $ Ksb {rm a} rm s $接近暴露的组氨酸（6.6）。 His-48和-113降低了p $ Ksb {rm a} $ s，表明本地环境有利于中立国。 His-36的p $ Ksb {rm a} $（$> $ 7.5）高，这意味着与负电荷有很强的相互作用。即使在低pH值下，His-24和82也以中性状态被掩埋。 His-119具有相对正常的p $ Ksb {rm a} $，但是与His-24的氢键增加了电离过程的复杂性。 His-12和His-48的滴定度不能用X射线结构解释。 His-113的p $ Ksb {rm a} $对盐浓度（0.2 M和1.5 M NaCl）的依赖性最大。改变盐浓度不会明显影响His-36和-48的p $ Ksb {rm a} $。其他组氨酸的p $ Ksb {rm a} $随盐浓度的增加而略有增加，表明具有简单的离子屏蔽作用。收集了关于马超肌红蛋白的类似数据。

著录项

  • 作者

    Kao, Yung-Hsiang.;

  • 作者单位

    The Pennsylvania State University.;

  • 授予单位 The Pennsylvania State University.;
  • 学科 Biophysics.;Physical chemistry.;Biochemistry.
  • 学位 Ph.D.
  • 年度 1994
  • 页码 260 p.
  • 总页数 260
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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