Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.
Department of Biochemistry & Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.
Proc Natl Acad Sci U S A. 2018 Oct 23;115(43):10965-10970. doi: 10.1073/pnas.1810054115. Epub 2018 Oct 9.
Protein-protein interactions are usually studied in dilute buffered solutions with macromolecule concentrations of <10 g/L. In cells, however, the macromolecule concentration can exceed 300 g/L, resulting in nonspecific interactions between macromolecules. These interactions can be divided into hard-core steric repulsions and "soft" chemical interactions. Here, we test a hypothesis from scaled particle theory; the influence of hard-core repulsions on a protein dimer depends on its shape. We tested the idea using a side-by-side dumbbell-shaped dimer and a domain-swapped ellipsoidal dimer. Both dimers are variants of the B1 domain of protein G and differ by only three residues. The results from the relatively inert synthetic polymer crowding molecules, Ficoll and PEG, support the hypothesis, indicating that the domain-swapped dimer is stabilized by hard-core repulsions while the side-by-side dimer shows little to no stabilization. We also show that protein cosolutes, which interact primarily through nonspecific chemical interactions, have the same small effect on both dimers. Our results suggest that the shape of the protein dimer determines the influence of hard-core repulsions, providing cells with a mechanism for regulating protein-protein interactions.
蛋白质-蛋白质相互作用通常在稀缓冲溶液中进行，大分子浓度<10 g/L。然而，在细胞中，大分子浓度可超过 300 g/L，导致大分子之间发生非特异性相互作用。这些相互作用可以分为硬核心排斥和“软”化学相互作用。在这里，我们检验了从标度粒子理论中得出的一个假设；硬核心排斥对蛋白质二聚体的影响取决于其形状。我们使用并排哑铃形二聚体和交换域的椭圆形二聚体来检验这一想法。这两种二聚体都是蛋白 G 的 B1 结构域的变体，仅相差三个残基。来自相对惰性的合成聚合物拥挤分子（Ficoll 和 PEG）的结果支持了这一假设，表明交换域的二聚体通过硬核心排斥稳定，而并排的二聚体几乎没有稳定作用。我们还表明，主要通过非特异性化学相互作用相互作用的蛋白质共溶剂对这两种二聚体都有相同的小影响。我们的结果表明，蛋白质二聚体的形状决定了硬核心排斥的影响，为细胞提供了一种调节蛋白质-蛋白质相互作用的机制。
