Institut de Biologie et de Technologies de Saclay/Service de Bioénergétique, Biologie Structurale et Mécanismes, Commissariat à l'Énergie Atomique et aux Énergies Alternatives-Saclay, 91191 Gif-sur-Yvette, France.
J Am Chem Soc. 2012 Jan 11;134(1):723-33. doi: 10.1021/ja210299g. Epub 2011 Dec 22.
Among noncovalent forces, electrostatic ones are the strongest and possess a rather long-range action. For these reasons, charges and counterions play a prominent role in self-assembly processes in water and therefore in many biological systems. However, the complexity of the biological media often hinders a detailed understanding of all the electrostatic-related events. In this context, we have studied the role of charges and counterions in the self-assembly of lanreotide, a cationic octapeptide. This peptide spontaneously forms monodisperse nanotubes (NTs) above a critical concentration when solubilized in pure water. Free from any screening buffer, we assessed the interactions between the different peptide oligomers and counterions in solutions, above and below the critical assembly concentration. Our results provide explanations for the selection of a dimeric building block instead of a monomeric one. Indeed, the apparent charge of the dimers is lower than that of the monomers because of strong chemisorption. This phenomenon has two consequences: (i) the dimer-dimer interaction is less repulsive than the monomer-monomer one and (ii) the lowered charge of the dimeric building block weakens the electrostatic repulsion from the positively charged NT walls. Moreover, additional counterion condensation (physisorption) occurs on the NT wall. We furthermore show that the counterions interacting with the NTs play a structural role as they tune the NTs diameter. We demonstrate by a simple model that counterions adsorption sites located on the inner face of the NT walls are responsible for this size control.
在非共价力中，静电相互作用力最强，作用范围也相当大。由于这些原因，电荷和抗衡离子在水相中的自组装过程中起着重要作用，因此在许多生物体系中也是如此。然而，生物介质的复杂性往往阻碍了对所有静电相关事件的详细了解。在这种情况下，我们研究了电荷和抗衡离子在兰瑞肽（一种阳离子八肽）自组装中的作用。当该肽在纯水中溶解时，其浓度超过临界浓度就会自发形成单分散的纳米管（NTs）。在没有任何屏蔽缓冲液的情况下，我们评估了不同肽低聚物和抗衡离子在溶液中的相互作用，包括高于和低于临界组装浓度的情况。我们的研究结果为选择二聚体作为构建基元而不是单体提供了合理的解释。事实上，由于强化学吸附作用，二聚体的表观电荷比单体的要低。这种现象有两个后果：（i）二聚体-二聚体的相互作用比单体-单体的相互作用的排斥力小；（ii）二聚体构建基元的电荷降低会减弱来自带正电荷的 NT 壁的静电排斥。此外，还会在 NT 壁上发生额外的抗衡离子缩合（物理吸附）。此外，我们还表明与 NT 相互作用的抗衡离子起到了结构调节作用，因为它们可以调节 NT 的直径。我们通过一个简单的模型证明，位于 NT 壁内表面的抗衡离子吸附位是这种尺寸控制的原因。
