Heat capacities and a snapshot of the energy landscape in protein GB1 from the pre-denaturation temperature dependence of backbone NH nanosecond fluctuations.
Heat capacities and a snapshot of the energy landscape in protein GB1 from the pre-denaturation temperature dependence of backbone NH nanosecond fluctuations.
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DOI：
10.1016/s0022-2836(02)01155-5
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发表时间：
2003-01
影响因子：
5.6
通讯作者：
D. Idiyatullin;I. Nesmelova;V. Daragan;K. Mayo
中科院分区：
文献类型：
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作者：
D. Idiyatullin;I. Nesmelova;V. Daragan;K. Mayo
蛋白质的稳定性通常用熔化温度和相关的热力学参数来量热表征。尽管它的重要性，微观起源的熔融转变和热力学稳定性和动力学之间的关系仍然是一个谜。本文在5-50℃的预变性温度范围内，获得了链球菌蛋白G的56个残基免疫球蛋白结合域的骨架15nh基团的核磁共振弛豫参数。采用三种方法对松弛数据进行分析：标准的三洛伦兹模型自由方法；F(ω)=2ωJ（ω）频谱密度方法，产生运动相关时间分布，以及确定频率相关阶参量的新方法。无论采用何种分析方法，内部运动相关次数和阶数参数对温度的依赖性本质上是相同的。蛋白质中所有的NHs都有纳秒级的内部运动，它们的温度依赖性产生的活化能高达约33kJ/摩尔残基。NH运动势垒高度在结构上是相关的，在褶皱最“刚性”的部分（β-链1和4以及α-螺旋）的残基中发现了最大的能量势垒。这一趋势也与从氢-氘（H-D）交换测量中得出的折叠展开的自由能相似，表明发生在纳秒时间尺度上的内部运动的能量反映了发生在更慢的H-D交换时间尺度上的能量。根据序参量的温度依赖性得出的余热容范围从接近零到接近100J/molKresidue，并与能量格局相关。这些结果提供了这种蛋白质能量格局的独特图景，以及热力学稳定性和动力学之间的关系，表明褶皱中的热敏区域可能启动熔化过程。
Protein stability is usually characterized calorimetrically by a melting temperature and related thermodynamic parameters. Despite its importance, the microscopic origin of the melting transition and the relationship between thermodynamic stability and dynamics remains a mystery. Here, NMR relaxation parameters were acquired for backbone15NH groups of the 56 residue immunoglobulin-binding domain of streptococcal protein G over a pre-denaturation temperature range of 5–50°C. Relaxation data were analyzed using three methods: the standard three-Lorentzian model free approach; the F(ω)=2ωJ(ω) spectral density approach that yields motional correlation time distributions, and a new approach that determines frequency-dependent order parameters. Regardless of the method of analysis, the temperature dependence of internal motional correlation times and order parameters is essentially the same. Nanosecond time-scale internal motions are found for all NHs in the protein, and their temperature dependence yields activation energies ranging up to about 33kJ/molresidue. NH motional barrier heights are structurally correlated, with the largest energy barriers being found for residues in the most “rigid” segments of the fold: β-strands 1 and 4 and the α-helix. Trends in this landscape also parallel the free energy of folding–unfolding derived from hydrogen–deuterium (H–D) exchange measurements, indicating that the energetics for internal motions occurring on the nanosecond time-scale mirror those occurring on the much slower time-scale of H–D exchange. Residual heat capacities, derived from the temperature dependence of order parameters, range from near zero to near 100J/molKresidue and correlate with this energy landscape. These results provide a unique picture of this protein's energy landscape and a relationship between thermodynamic stability and dynamics that suggests thermosensitive regions in the fold that could initiate the melting process.