Department of Biochemistry, University of Zurich, Zurich 8057, Switzerland.
Department of Physical Sciences and Centre for Advanced Functional Materials, Indian Institute of Science Education and Research Kolkata, Mohanpur 741246, India.
Proc Natl Acad Sci U S A. 2023 Oct 10;120(41):e2304036120. doi: 10.1073/pnas.2304036120. Epub 2023 Oct 5.
Highly disordered complexes between oppositely charged intrinsically disordered proteins present a new paradigm of biomolecular interactions. Here, we investigate the driving forces of such interactions for the example of the highly positively charged linker histone H1 and its highly negatively charged chaperone, prothymosin α (ProTα). Temperature-dependent single-molecule Förster resonance energy transfer (FRET) experiments and isothermal titration calorimetry reveal ProTα-H1 binding to be enthalpically unfavorable, and salt-dependent affinity measurements suggest counterion release entropy to be an important thermodynamic driving force. Using single-molecule FRET, we also identify ternary complexes between ProTα and H1 in addition to the heterodimer at equilibrium and show how they contribute to the thermodynamics observed in ensemble experiments. Finally, we explain the observed thermodynamics quantitatively with a mean-field polyelectrolyte theory that treats counterion release explicitly. ProTα-H1 complex formation resembles the interactions between synthetic polyelectrolytes, and the underlying principles are likely to be of broad relevance for interactions between charged biomolecules in general.
带相反电荷的固有无序蛋白质之间高度无序的复合物呈现出生物分子相互作用的新范例。在这里，我们以高度带正电荷的连接组蛋白 H1 及其高度带负电荷的伴侣蛋白 prothymosin α（ProTα）为例，研究这种相互作用的驱动力。温度依赖性单分子Förster 共振能量转移（FRET）实验和等温热滴定法表明，ProTα-H1 结合在焓不利，盐依赖性亲和力测量表明抗衡离子释放熵是一个重要的热力学驱动力。使用单分子 FRET，我们还鉴定了 ProTα 和 H1 之间的三元复合物，除了平衡时的异二聚体外，并展示了它们如何有助于在整体实验中观察到的热力学。最后，我们使用平均场聚电解质理论对观察到的热力学进行定量解释，该理论明确地处理抗衡离子的释放。ProTα-H1 复合物的形成类似于合成聚电解质之间的相互作用，其潜在原理可能对一般带电荷生物分子之间的相互作用具有广泛的相关性。
