It is now well appreciated that the crowded intracellular environment significantly modulates an array of physiological processes including protein folding-unfolding, aggregation, and dynamics to name a few. In this work we have studied the dynamics of domain I of the protein human serum albumin (HSA) in its urea-induced denatured states, in the presence of a series of commonly used macromolecular crowding agents. HSA was labeled at Cys-34 (a free cysteine) in domain I with the fluorophore 6-bromoacetyl-2-dimethylaminonaphthalene (BADAN) to act as a solvation probe. In partially denatured states (2-6 M urea), lower crowder concentrations (~ < 125 g/L) induced faster dynamics, while the dynamics became slower beyond 150 g/L of crowders. We propose that this apparent switch in dynamics is an evidence of a crossover from soft (enthalpic) to hard-core (entropic) interactions between the protein and crowder molecules. That soft interactions are also important for the crowders used here was further confirmed by the appreciable shift in the wavelength of the emission maximum of BADAN, in particular for PEG8000 and Ficoll 70 at concentrations where the excluded volume effect is not dominant.

中文翻译：

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拥挤剂对变性状态下多域蛋白动力学的影响：一种溶剂化方法。

现在众所周知，拥挤的细胞内环境显着调节了一系列生理过程，包括蛋白质折叠-展开，聚集和动力学等。在这项工作中，我们研究了在一系列常用的大分子拥挤剂的存在下，人血清白蛋白（HSA）蛋白质结构域I在尿素诱导的变性状态下的动力学。HSA在结构域I的Cys-34（游离半胱氨酸）处标记有荧光团6-溴乙酰基-2-二甲基氨基萘（BADAN），用作溶剂化探针。在部分变性状态（2-6 M尿素）下，较低的拥挤物浓度（〜<125 g / L）引起较快的动力学，而在超过150 g / L的拥挤物时动力学变慢。我们认为，这种动力学上的明显转变是蛋白质与拥挤分子之间从软（焓）相互作用向硬核（熵）相互作用的证明。BADAN的最大发射波长的明显变化进一步证实了软相互作用对此处使用的拥挤者也很重要，特别是对于浓度不占优势的PEG8000和Ficoll 70。