Flexible, charged biopolymers in monovalent and mixed-valence salt: Regimes of anomalous electrostatic stiffening and of salt insensitivity
Flexible, charged biopolymers in monovalent and mixed-valence salt: Regimes of anomalous electrostatic stiffening and of salt insensitivity
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单价和混合价盐中的柔性带电生物聚合物：异常静电硬化和盐不敏感性的机制
DOI：
10.1103/physreve.104.014504
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发表时间：
2021
影响因子：
2.4
通讯作者：
Saleh, Omar A.
中科院分区：
文献类型：
--
作者：
Innes-Gold, Sarah N.;Jacobson, David R.;Pincus, Philip A.;Stevens, Mark J.;Saleh, Omar A.
生物聚电解质（PE）的构象，如多糖，蛋白质和核酸，影响它们的行为和与其他生物分子的相互作用。相对于中性聚合物，溶液中的PE由于链内静电排斥而更具局部刚性，其大小取决于添加的盐的浓度。这通常使用Odijk-Skolnick-Fixman（OSF）静电硬化模型进行量化，其中盐依赖性Debye-Hückel（DH）筛选调节链内排斥。然而，这种方法对灵活PE的适用性长期以来一直受到质疑。为了研究这一点，我们使用高精度的单分子弹性测量来推断三种柔性生物聚合物（透明质酸，单链RNA和单链DNA）在单价和混合价盐溶液中的局部刚度与盐的缩放。在单价盐，我们崩溃的数据在所有三种聚合物占电荷间距，并找到一个共同的幂律缩放的静电持久性长度与离子强度的指数。这一结果排除了静电硬化的简单OSF图片。它与Netz和奥兰提出的修正的OSF图大致一致;或者，如果相关的静电屏蔽长度是绝缘间距而不是DH长度，则可以解释该指数。在混合盐溶液中，我们发现在多价盐的存在下添加单价盐不会影响PE刚度的方案。使用粗粒度的模拟，和一个三态模型的凝聚，链接近，和散装离子，我们把这个政权的“夹克”的离子周围的PE，调节链的有效电荷密度作为离子强度的变化。在模拟中，该导管架的尺寸再次与由绝缘间距控制的屏蔽长度一致，而不是DH长度。两者合计，我们的研究结果描述了一个统一的图片的聚电解质的静电刚度的混合价盐的条件下，直接相关的细胞和细胞间的生物系统。
The conformations of biological polyelectrolytes (PEs), such as polysaccharides, proteins, and nucleic acids, affect how they behave and interact with other biomolecules. Relative to neutral polymers, PEs in solution are more locally rigid due to intrachain electrostatic repulsion, the magnitude of which depends on the concentration of added salt. This is typically quantified using the Odijk-Skolnick-Fixman (OSF) electrostatic-stiffening model, in which salt-dependent Debye-Hückel (DH) screening modulates intrachain repulsion. However, the applicability of this approach to flexible PEs has long been questioned. To investigate this, we use high-precision single-molecule elasticity measurements to infer the scaling with salt of the local stiffness of three flexible biopolymers (hyaluronic acid, single-stranded RNA, and single-stranded DNA) in both monovalent and mixed-valence salt solutions. In monovalent salt, we collapse the data across all three polymers by accounting for charge spacing, and find a common power-law scaling of the electrostatic persistence length with ionic strength with an exponent of. This result rules out simple OSF pictures of electrostatic stiffening. It is roughly compatible with a modified OSF picture developed by Netz and Orland; alternatively, we posit the exponent can be explained if the relevant electrostatic screening length is the interion spacing rather than the DH length. In mixed salt solutions, we find a regime where adding monovalent salt, in the presence of multivalent salt, does not affect PE stiffness. Using coarse-grained simulations, and a three-state model of condensed, chain-proximate, and bulk ions, we attribute this regime to a “jacket” of ions surrounding the PE that regulates the chain's effective charge density as ionic strength varies. The size of this jacket in simulations is again consistent with a screening length controlled by interion spacing rather than the DH length. Taken together, our results describe a unified picture of the electrostatic stiffness of polyelectrolytes in the mixed-valence salt conditions of direct relevance to cellular and intercellular biological systems.