Sjöberg B, Pap S, Kjems J
Eur J Biochem. 1987 Jan 15;162(2):259-64. doi: 10.1111/j.1432-1033.1987.tb10593.x.
The dodecylsulfate-induced dissociation of the tetrameric alpha 2-macroglobulin molecule from human plasma has been investigated by the small-angle neutron scattering (SANS) method. The great advantage with the SANS method is that, by using deuterated dodecylsulfate, and contrast variation by changing the D2O/H2O ratio of the solvent, we can selectively study just the protein part, or the dodecylsulfate part, of the protein-dodecylsulfate complex. More than a thousandfold excess of dodecylsulfate (on a molar basis) is needed in order to dissociate alpha 2-macroglobulin to particles with, on average, half the original molecular mass. By combining the SANS data with results obtained by the equilibrium dialysis technique it follows that, under these circumstances, approximately one thousand dodecylsulfate molecules are associated per alpha 2-macroglobulin molecule. From the significant increase in the radius of gyration, which accompanies the dissociation process, we can conclude that the dissociation is associated with a drastic change in conformation of the protein molecule. From measurements where the dodecylsulfate part of the complex dominates the SANS signal we also get an indication that the dodecylsulfate is randomly distributed along the polypeptide chain, rather than being arranged in large clusters at certain regions of the protein molecule. By fitting the parameters of a binding model to the experimental data we obtain the result that most of the more than one thousand bound dodecylsulfate molecules, necessary for dissociation, are involved in the change in conformation, and the dissociation process is, in fact, driven by the binding of a very few extra dodecylsulfate molecules to the dissociation products. These data indicate that the dodecylsulfate-induced dissociation of alpha 2-macroglobulin is probably more complicated than just breaking, for instance, a hydrophobic interaction.
采用小角中子散射（SANS）方法研究了十二烷基硫酸盐诱导人血浆中四聚体α2-巨球蛋白分子的解离。SANS方法的一大优势在于，通过使用氘代十二烷基硫酸盐，并通过改变溶剂的D2O/H2O比例来实现对比变化，我们可以选择性地研究蛋白质-十二烷基硫酸盐复合物中仅蛋白质部分或十二烷基硫酸盐部分。为了将α2-巨球蛋白解离成平均分子量为原来一半的颗粒，需要摩尔比超过一千倍的十二烷基硫酸盐。通过将SANS数据与平衡透析技术获得的结果相结合可知，在这些情况下，每个α2-巨球蛋白分子大约有一千个十二烷基硫酸盐分子与之结合。从解离过程中伴随的回转半径显著增加，我们可以得出结论，解离与蛋白质分子构象的剧烈变化有关。从复合物中十二烷基硫酸盐部分主导SANS信号的测量结果中我们还得到一个迹象，即十二烷基硫酸盐沿着多肽链随机分布，而不是在蛋白质分子的某些区域聚集成大的簇。通过将结合模型的参数拟合到实验数据中，我们得到的结果是，解离所需的一千多个结合的十二烷基硫酸盐分子中的大多数参与了构象变化，实际上，解离过程是由极少数额外的十二烷基硫酸盐分子与解离产物的结合驱动的。这些数据表明，十二烷基硫酸盐诱导的α2-巨球蛋白解离可能比仅仅破坏例如疏水相互作用更为复杂。
