血红素丙酸基团对马心脏肌红蛋白中与一氧化碳光解离相关的构象动力学的贡献。
The contribution of heme propionate groups to the conformational dynamics associated with CO photodissociation from horse heart myoglobin.
作者信息
Belogortseva Natalia, Rubio Marisa, Terrell William, Miksovská Jaroslava
机构信息
Chemistry Department, Marshall University, One John Marshall Drive, Huntington, WV 25755, USA.
出版信息
J Inorg Biochem. 2007 Jul;101(7):977-86. doi: 10.1016/j.jinorgbio.2007.03.009. Epub 2007 Apr 2.
Photoacoustic calorimetry and transient absorption spectroscopy were used to study conformational dynamics associated with CO photodissociation from horse heart myoglobin (Mb) reconstituted with either Fe protoporphyrin IX dimethylester (FePPDME), Fe octaethylporphyrin (FeOEP), or with native Fe protoporphyrin IX (FePPIX). The volume and enthalpy changes associated with the Fe-CO bond dissociation and formation of a transient deoxyMb intermediate for the reconstituted Mbs were found to be similar to those determined for native Mb (DeltaV1 = -2.5+/-0.6 ml mol(-1) and DeltaH1 = 8.1+/-3.0 kcal mol(-1)). The replacement of FePPIX by FeOEP significantly alters the conformational dynamics associated with CO release from protein. Ligand escape from FeOEP reconstituted Mb was determined to be roughly a factor of two faster (tau=330 ns) relative to native protein (tau=700 ns) and accompanying reaction volume and enthalpy changes were also found to be smaller (DeltaV2 = 5.4+/-2.5 ml mol(-1) and DeltaH2 = 0.7+/-2.2 kcal mol(-1)) than those for native Mb (DeltaV2 = 14.3+/-0.8 ml mol(-1) and DeltaH2 = 7.8+/-3.5 kcal mol(-1)). On the other hand, volume and enthalpy changes for CO release from FePPIX or FePPDME reconstituted Mb were nearly identical to those of the native protein. These results suggest that the hydrogen bonding network between heme propionate groups and nearby amino acid residues likely play an important role in regulating ligand diffusion through protein matrix. Disruption of this network leads to a partially open conformation of protein with less restricted ligand access to the heme binding pocket.
采用光声量热法和瞬态吸收光谱法研究了用亚铁原卟啉IX二甲酯（FePPDME）、八乙基卟啉铁（FeOEP）或天然亚铁原卟啉IX（FePPIX）重构的马心肌红蛋白（Mb）中与CO光解离相关的构象动力学。发现重构的肌红蛋白中与Fe-CO键解离以及形成瞬态脱氧肌红蛋白中间体相关的体积和焓变与天然肌红蛋白所测定的结果相似（ΔV1 = -2.5±0.6 ml mol⁻¹，ΔH1 = 8.1±3.0 kcal mol⁻¹）。用FeOEP替代FePPIX会显著改变与蛋白质中CO释放相关的构象动力学。相对于天然蛋白质（τ = 700 ns），从FeOEP重构的肌红蛋白中配体逸出的速度大约快两倍（τ = 330 ns），并且还发现伴随的反应体积和焓变更小（ΔV2 = 5.4±2.5 ml mol⁻¹，ΔH2 = 0.7±2.2 kcal mol⁻¹），而天然肌红蛋白的相应值为（ΔV2 = 14.3±0.8 ml mol⁻¹，ΔH2 = 7.8±3.5 kcal mol⁻¹）。另一方面，从FePPIX或FePPDME重构的肌红蛋白中释放CO的体积和焓变与天然蛋白质几乎相同。这些结果表明，血红素丙酸基团与附近氨基酸残基之间的氢键网络可能在调节配体通过蛋白质基质的扩散中起重要作用。该网络的破坏导致蛋白质形成部分开放的构象，使配体进入血红素结合口袋的限制减少。
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