Insulin receptor (IR) signaling controls multiple facets of animal physiology. Maximally four insulins bind to IR at two distinct sites, termed site-1 and site-2. However, the precise functional roles of each binding event during IR activation remain unresolved. Here, we showed that IR incompletely saturated with insulin predominantly forms an asymmetric conformation and exhibits partial activation. IR with one insulin bound adopts a Γ-shaped conformation. IR with two insulins bound assumes a Ƭ-shaped conformation. One insulin binds at site-1 and another simultaneously contacts both site-1 and site-2 in the Ƭ-shaped IR dimer. We further show that concurrent binding of four insulins to sites-1 and -2 prevents the formation of asymmetric IR and promotes the T-shaped symmetric, fully active state. Collectively, our results demonstrate how the synergistic binding of multiple insulins promotes optimal IR activation.

胰岛素受体 (IR) 信号控制着动物生理学的多个方面。最多有四种胰岛素在两个不同的位点与 IR 结合，称为位点 1 和位点 2。然而，IR 激活过程中每个绑定事件的确切功能角色仍未解决。在这里，我们发现胰岛素不完全饱和的 IR 主要形成不对称构象并表现出部分激活。与一种胰岛素结合的 IR 采用 Γ 形构象。结合两个胰岛素的 IR 呈现Ƭ形构象。一种胰岛素在 site-1 结合，另一种同时接触Ƭ中的 site-1 和 site-2形红外二聚体。我们进一步表明，四种胰岛素与位点 1 和 -2 的同时结合可防止不对称 IR 的形成并促进 T 形对称、完全活跃状态。总的来说，我们的结果证明了多种胰岛素的协同结合如何促进最佳的 IR 激活。