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首页> 外文期刊>Biochemistry >Global structure analysis of acid-unfolded myoglobin with consideration to effects of intermolecular coulomb repulsion on solution X-ray scattering
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Global structure analysis of acid-unfolded myoglobin with consideration to effects of intermolecular coulomb repulsion on solution X-ray scattering

机译：考虑到分子间库仑排斥对溶液X射线散射的影响，酸解折叠的肌红蛋白的整体结构分析

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摘要

To obtain information on the global structure of protein in the acid-unfolded (AU) state, the structure of apomyoglobin (apoMb) was analyzed by using the solution X-ray scattering (SXS) method. SXS profiles were obtained over a wide range of protein concentrations, 1-18 mg mL(-1), under strongly acidic conditions. From analysis of the SXS profile extrapolated to a zero protein concentration, the mean square radius, R-sq, of AU-apoMb at 20 mM HCl was estimated to be 4.81 +/- 0.31 nm. This estimate is more than 1.3 nm larger than those of 3.0-3.5 nm reported thus far. The difference originates from the fact that effects of Coulomb repulsive forces acting between AU-apoMb molecules have not been correctly taken into account in the conventional analysis. In fact, even at a low protein concentration of 1 mg mL(-1) close to the limit of measurement in the present SXS method, the solution condition applicable to estimating accurately structural parameters of AU-apoMb is very limited. At HCl concentrations lower than 10 mM, the scattering intensity at a small scattering vector decreases remarkably through the effect of intermolecular repulsive forces and the forward scattering intensity is significantly lower than the estimate from the partial specific volume of protein. On the other hand, at HCl concentrations higher than 50 mM, some compact molten-globule-like structures emerge. As a result, the intermediate concentration of 20 mM HCl is the best choice of the solution condition for determining R-sq of AU-apoMb. The effect of intermolecular Coulomb repulsion on the SXS profile of AU-apoMb is at its maximum for forward scattering and decreases monotonously with an increase in the scattering angle to be virtually negligible at K approximate to 0.63 nm(-1). Whereas urea-denatured apoMb shows a SXS profile typical of Gaussian chains, the intrinsic SXS profile of AU-apoMb differs significantly from those of Gaussian chains.
机译：为了获得有关酸未折叠（AU）状态下蛋白质整体结构的信息，使用溶液X射线散射（SXS）方法分析了肌红蛋白（apoMb）的结构。在强酸性条件下，在宽范围的蛋白质浓度（1-18 mg mL（-1））中获得了SXS图。根据外推至蛋白质浓度为零的SXS谱图分析，在20 mM HCl下AU-apoMb的均方半径R-sq估计为4.81 +/- 0.31 nm。该估计值比迄今为止报道的3.0-3.5 nm估计值大1.3 nm以上。差异源于以下事实：在常规分析中未正确考虑到AU-apoMb分子之间作用的库仑排斥力的影响。实际上，即使在接近当前SXS方法中测量极限的1 mg mL（-1）的低蛋白浓度下，适用于准确估算AU-apoMb结构参数的溶液条件也非常有限。在HCl浓度低于10 mM时，小的散射矢量的散射强度会由于分子间排斥力的作用而显着降低，并且正向散射强度显着低于蛋白质部分比容的估计值。另一方面，在HCl浓度高于50 mM时，会出现一些紧密的熔融球状结构。结果，20 mM HCl的中间浓度是确定AU-apoMb的R-sq的溶液条件的最佳选择。分子间库仑斥力对AU-apoMb的SXS分布的影响最大，对于正向散射，随着散射角的增加而单调减少，在K大约为0.63 nm（-1）时几乎可以忽略不计。尿素变性的apoMb表现出高斯链的典型SXS谱，而AU-apoMb的固有SXS谱与高斯链的SXS谱显着不同。

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