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Abstract：
In the protein purification, drug delivery, food industry, and biotechnological applications involving protein-polyelectrolyte complexation, proper selection of co-solutes and solution conditions plays a crucial role. The onset of (bio)macromolecular complexation occurs even on the so-called \"wrong side\" of the protein isoionic point where both the protein and the polyelectrolyte are net like-charged. To gain mechanistic insights into the modulatory role of salts (NaCl, NaBr, and NaI) and sugars (sucrose and sucralose) in protein-polyelectrolyte complexation under such conditions, interaction between bovine serum albumin (BSA) and sodium polystyrene sulfonate (NaPSS) at pH = 8.0 was studied by a combination of isothermal titration calorimetry, fluorescence spectroscopy, circular dichroism, and thermodynamic modeling. The BSA-NaPSS complexation proceeds by two binding processes (first, formation of intrapolymer complexes and then formation of interpolymer complexes), both driven by favorable electrostatic interactions between the negatively charged sulfonic groups (-SO3-) of NaPSS and positively charged patches on the BSA surface. Two such positive patches were identified, each responsible for one of the two binding processes. The presence of salts screened both short-range attractive and long-range repulsive electrostatic interactions between both macromolecules, resulting in a nonmonotonic dependence of the binding affinity on the total ionic strength for both binding processes. In addition, distinct anion-specific effects were observed (NaCl < NaBr < NaI). The effect of sugars was less pronounced: sucrose had no effect on the complexation, but its chlorinated analogue, sucralose, promoted it slightly due to the screening of long-range repulsive electrostatic interactions between BSA and NaPSS. Although short-range non-electrostatic interactions are frequently mentioned in the literature in relation to BSA or NaPSS, we found that the main driving force of complexation on the \"wrong side\" are electrostatic interactions.
摘要：
在蛋白质纯化中，药物输送,食品工业,以及涉及蛋白质-聚电解质络合的生物技术应用，正确选择共溶质和溶液条件起着至关重要的作用。（生物）大分子络合的开始甚至发生在蛋白质等离子点的所谓“错误的一侧”，在该位置，蛋白质和聚电解质都带网状电荷。为了获得对盐(NaCl，NaBr,和NaI）和糖（蔗糖和三氯蔗糖）在这种条件下的蛋白质-聚电解质络合，牛血清白蛋白（BSA）和聚苯乙烯磺酸钠（NaPSS）之间的相互作用在pH=8.0进行了联合等温滴定量热法研究，荧光光谱法，圆二色性,和热力学建模。BSA-NaPSS络合通过两个结合过程(首先，形成聚合物内复合物，然后形成聚合物间复合物)，两者都由NaPSS的带负电荷的磺酸基（-SO3-）和BSA表面上的带正电荷的贴片之间的有利的静电相互作用驱动。确定了两个这样的阳性斑块，每个负责两个绑定过程之一。盐的存在筛选了两个大分子之间的短程吸引和长程排斥静电相互作用，导致两种结合过程的结合亲和力对总离子强度的非单调依赖性。此外,观察到明显的阴离子特异性效应(NaCl
