目的:非离子表面活性剂可以对抗阴离子表面活性剂对蛋白质的有害影响,其中从先前展开的状态检索折叠状态。然而,需要进一步的研究来完善我们对重折叠过程的潜在机制的理解。虽然非离子表面活性剂和紧密折叠的蛋白质之间的相互作用不是预期的,我们假设表面活性剂诱导的去折叠的中间阶段可以定义新的相互作用机制,通过这些机制,非离子表面活性剂可以进一步改变蛋白质的构象。
方法:在这项工作中,三种模型蛋白质的行为(人类生长激素,牛血清白蛋白,和β-乳球蛋白)在阴离子表面活性剂十二烷基硫酸钠的存在下进行了研究,非离子表面活性剂β-十二烷基麦芽糖苷,和两种表面活性剂的混合物。使用固有荧光光谱法和远UV圆二色性确定蛋白质发生的转变。基于这些结果,我们开发了一个详细的人类生长激素相互作用模型.利用核磁共振和对比度变化的小角度中子散射,我们研究了氨基酸环境和蛋白质的构象状态。
结果:结果证明了表面活性剂合作在确定蛋白质构象状态方面的关键作用,根据非离子表面活性剂与离子表面活性剂的比例,可以偏离或朝向折叠状态。十二烷基麦芽糖苷,最初是一种非相互作用的表面活性剂,可以出乎意料地与十二烷基硫酸钠展开的蛋白质缔合,以在低的非离子表面活性剂与离子表面活性剂比率下进一步影响它们的构象。当这个比率增加时,蛋白质开始恢复折叠状态。然而,由于残留的表面活性剂分子仍吸附在蛋白质上,因此天然构象无法完全恢复。这项研究表明,蛋白质的构象景观取决于表面活性剂之间的微妙相互作用,最终由它们之间的比例控制,导致蛋白质构象发生不可预测的变化。
OBJECTIVE: Nonionic surfactants can counter the deleterious effect that anionic surfactants have on proteins, where the folded states are retrieved from a previously unfolded state. However, further studies are required to refine our understanding of the underlying mechanism of the refolding process. While interactions between nonionic surfactants and tightly folded proteins are not anticipated, we hypothesized that intermediate stages of surfactant-induced unfolding could define new interaction mechanisms by which nonionic surfactants can further alter protein conformation.
METHODS: In this work, the behavior of three model proteins (human growth hormone, bovine serum albumin, and β-lactoglobulin) was investigated in the presence of the anionic surfactant sodium dodecylsulfate, the nonionic surfactant β-dodecylmaltoside, and mixtures of both surfactants. The transitions occurring to the proteins were determined using intrinsic fluorescence spectroscopy and far-UV circular dichroism. Based on these results, we developed a detailed interaction model for human growth hormone. Using nuclear magnetic resonance and contrast-variation small-angle neutron scattering, we studied the amino acid environment and the conformational state of the protein.
RESULTS: The results demonstrate the key role of surfactant cooperation in defining the conformational state of the proteins, which can shift away or toward the folded state depending on the nonionic-to-ionic surfactant ratio. Dodecylmaltoside, initially a non-interacting surfactant, can unexpectedly associate with sodium dodecylsulfate-unfolded proteins to further impact their conformation at low nonionic-to-ionic surfactant ratio. When this ratio increases, the protein begins to retrieve the folded state. However, the native conformation cannot be fully recovered due to remnant surfactant molecules still adsorbed to the protein. This study demonstrates that the conformational landscape of the protein depends on a delicate interplay between the surfactants, ultimately controlled by the ratio between them, resulting in unpredictable changes in the protein conformation.