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首页> 外文期刊>Biochemistry >Differences between the pressure- and temperature-induced denaturation and aggregation of beta-lactoglobulin A, B, and AB monitored by FT-IR spectroscopy and small-angle X-ray scattering.
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Differences between the pressure- and temperature-induced denaturation and aggregation of beta-lactoglobulin A, B, and AB monitored by FT-IR spectroscopy and small-angle X-ray scattering.

机译：β-乳球蛋白A，B和AB的压力和温度诱导的变性和聚集之间的差异通过FT-IR光谱法和小角度X射线散射监测。

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摘要

We examined the temperature- and pressure-induced unfolding and aggregation of beta-lactoglobulin (beta-Lg) and its genetic variants A and B up to temperatures of 90 degrees C in the pressure range from 1 bar to 10 kbar. To achieve information simultaneously on the secondary, tertiary, and quaternary structures, we have applied Synchrotron small-angle X-ray diffraction and Fourier transform infrared spectroscopy. Upon heating a beta-Lg solution at pH 7.0, the radius of gyration Rg first decreases, indicating a partial dissociation of the dimer into the monomers, the secondary structures remaining essentially unchanged. Above 50 degrees C, the infrared spectroscopy data reveal a decrease in intramolecular beta-sheet and alpha-helical structures, whereas the contribution of disordered structures increases. Within the temperature range from 50 to 60 degrees C, the appearance of the pair distance distribution function is not altered significantly, whereas the amount of defined secondary structures declines approximately by 10%. Above 60 degrees C the aggregation process of 1% beta-Lg solutions is clearly detectable by the increase in Rg and intermolecular beta-sheet content. The irreversible aggregation is due to intermolecular S-H/S-S interchange reactions and hydrophobic interactions. Upon pressurization at room temperature, the equilibrium between monomers and dimers is also shifted and dissociation of dimers is induced. At pressures of approximately 1300 bar, the amount of beta-sheet and alpha-helical structures decreases and the content of disordered structures increases, indicating the beginning unfolding of the protein which enables aggregation. Contrary to the thermal denaturation process, intermolecular beta-sheet formation is of less importance in pressure-induced protein aggregation and gelation. The spatial extent of the resulting protein clusters is time- and concentration-dependent. The aggregation of a 1% (w/w) solution of A, B, and the mixture AB results in the formation of at least octameric units as can be deduced from the radius of gyration of about 36 A. No differences in the pressure stability of the different genetic variants of beta-Lg are detectable in our FT-IR and SAXS experiments. Even application of higher pressures (up to 10 kbar) does not result in complete unfolding of all beta-Lg variants.
机译：我们检查了温度和压力诱导的β-乳球蛋白（β-Lg）及其遗传变异A和B的解折叠和聚集，直至温度在90摄氏度（1巴至10 kbar）下。为了同时获得有关二级，三级和四级结构的信息，我们应用了Synchrotron小角度X射线衍射和傅里叶变换红外光谱。在将pH 7.0的β-Lg溶液加热后，回转半径Rg首先减小，这表明二聚体部分解离成单体，二级结构基本上保持不变。高于50摄氏度时，红外光谱数据显示分子内β-折叠和α-螺旋结构减少，而无序结构的贡献增加。在50到60摄氏度的温度范围内，对距离分布函数的外观没有显着改变，而定义的二级结构的数量大约下降了10％。高于60摄氏度，通过Rg和分子间β-折叠含量的增加，很明显可以检测到1％β-Lg溶液的聚集过程。不可逆的聚集是由于分子间S-H / S-S交换反应和疏水相互作用。在室温下加压时，单体和二聚体之间的平衡也发生变化，并引起二聚体解离。在大约1300 bar的压力下，β-折叠和α-螺旋结构的数量减少，无序结构的含量增加，这表明蛋白质开始展开，从而能够聚集。与热变性过程相反，分子间β-折叠的形成在压力诱导的蛋白质聚集和胶凝中的重要性较小。所得蛋白质簇的空间范围是时间和浓度依赖性的。 A，B和混合物AB的1％（w / w）溶液的聚集导致至少八位单元的形成，这可以从约36 A的回转半径推导出。压力稳定性无差异在我们的FT-IR和SAXS实验中可以检测到β-Lg的不同遗传变异。即使施加更高的压力（最高10 kbar）也不会导致所有β-Lg变体完全展开。

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