Havel H A, Kauffman E W, Plaisted S M, Brems D N
Biochemistry. 1986 Oct 21;25(21):6533-8. doi: 10.1021/bi00369a029.
Previous investigations have shown that bovine growth hormone (bGH, somatotropin) unfolds through a reversible multistate process with at least one stable equilibrium intermediate. In extending our knowledge of the folding process for bGH, we demonstrate that a self-associated form of partially denatured bGH is formed during equilibrium unfolding experiments. The self-associated species has been identified by hydrodynamic measurements (size exclusion high-performance liquid chromatography and static and dynamic light scattering) and by measurements of the bGH concentration dependence of aromatic amino acid spectral properties (fluorescence, second-derivative absorption, and circular dichroism). The apparent maximum concentration for self-association occurs when bGH is partially denatured, i.e., at 3.7 M guanidine hydrochloride or 8.5 M urea, and its formation is reversible. Some of the properties of the self-associated species include quenched tryptophan fluorescence, increased tryptophan circular dichroism intensity at 300 nm, polar tryptophan environment, and a weight-average radius of about 5 nm. The self-association of bGH is mediated by specific intermolecular interactions with little increase in molecular size occurring above the saturation level of 4 mg/mL bGH. These phenomena have important implications for the design and interpretation of folding experiments in vitro and may have physiological consequences.
先前的研究表明，牛生长激素（bGH，生长激素）通过一个具有至少一个稳定平衡中间体的可逆多态过程展开。为了拓展我们对bGH折叠过程的认识，我们证明在平衡展开实验过程中会形成部分变性的bGH的一种自缔合形式。这种自缔合物种已通过流体动力学测量（尺寸排阻高效液相色谱以及静态和动态光散射）以及通过测量芳香族氨基酸光谱特性（荧光、二阶导数吸收和圆二色性）对bGH浓度的依赖性得以鉴定。自缔合的表观最大浓度出现在bGH部分变性时，即在3.7 M盐酸胍或8.5 M尿素中，并且其形成是可逆的。自缔合物种的一些特性包括色氨酸荧光猝灭、300 nm处色氨酸圆二色性强度增加、色氨酸极性环境以及约5 nm的重均半径。bGH的自缔合是由特定的分子间相互作用介导的，在bGH饱和水平4 mg/mL以上时分子大小几乎没有增加。这些现象对体外折叠实验的设计和解释具有重要意义，并且可能具有生理后果。
