Zhang Fajun, Skoda Maximilian W A, Jacobs Robert M J, Martin Richard A, Martin Christopher M, Schreiber Frank
Institut für Angewandte Physik, Universität Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany.
J Phys Chem B. 2007 Jan 11;111(1):251-9. doi: 10.1021/jp0649955.
We have studied a series of samples of bovine serum albumin (BSA) solutions with protein concentration, c, ranging from 2 to 500 mg/mL and ionic strength, I, from 0 to 2 M by small-angle X-ray scattering (SAXS). The scattering intensity distribution was compared to simulations using an oblate ellipsoid form factor with radii of 17 x 42 x 42 A, combined with either a screened Coulomb, repulsive structure factor, SSC(q), or an attractive square-well structure factor, SSW(q). At pH = 7, BSA is negatively charged. At low ionic strength, I < 0.3 M, the total interaction exhibits a decrease of the repulsive interaction when compared to the salt-free solution, as the net surface charge is screened, and the data can be fitted by assuming an ellipsoid form factor and screened Coulomb interaction. At moderate ionic strength (0.3-0.5 M), the interaction is rather weak, and a hard-sphere structure factor has been used to simulate the data with a higher volume fraction. Upon further increase of the ionic strength (I >or= 1.0 M), the overall interaction potential was dominated by an additional attractive potential, and the data could be successfully fitted by an ellipsoid form factor and a square-well potential model. The fit parameters, well depth and well width, indicate that the attractive potential caused by a high salt concentration is weak and long-ranged. Although the long-range, attractive potential dominated the protein interaction, no gelation or precipitation was observed in any of the samples. This is explained by the increase of a short-range, repulsive interaction between protein molecules by forming a hydration layer with increasing salt concentration. The competition between long-range, attractive and short-range, repulsive interactions accounted for the stability of concentrated BSA solution at high ionic strength.
我们通过小角X射线散射（SAXS）研究了一系列牛血清白蛋白（BSA）溶液样本，其蛋白质浓度c范围为2至500 mg/mL，离子强度I范围为0至2 M。将散射强度分布与使用扁椭球体形状因子（半径为17×42×42 Å）的模拟结果进行比较，该形状因子与屏蔽库仑排斥结构因子SSC(q)或吸引方阱结构因子SSW(q)相结合。在pH = 7时，BSA带负电荷。在低离子强度（I < 0.3 M）下，与无盐溶液相比，总相互作用表现出排斥相互作用的降低，因为净表面电荷被屏蔽，并且通过假设椭球体形状因子和屏蔽库仑相互作用可以拟合数据。在中等离子强度（0.3 - 0.5 M）下，相互作用相当弱，并且已使用硬球结构因子来模拟具有更高体积分数的数据。随着离子强度进一步增加（I≥1.0 M），整体相互作用势由额外的吸引势主导，并且通过椭球体形状因子和方阱势模型可以成功拟合数据。拟合参数阱深和阱宽表明，高盐浓度引起的吸引势较弱且范围较长。尽管长程吸引势主导了蛋白质相互作用，但在任何样本中均未观察到凝胶化或沉淀现象。这可以通过随着盐浓度增加形成水合层，蛋白质分子之间短程排斥相互作用的增加来解释。长程吸引和短程排斥相互作用之间的竞争解释了高离子强度下浓缩BSA溶液的稳定性。
