Ca²⁺/calmodulin dependent protein kinase II (CaMKII) is a signaling protein required for long-term memory. Once activated by Ca²⁺/CaM, it sustains activity even after the Ca²⁺ dissipates. In addition to well-known autophosphorylation-mediated mechanism, interaction with specific binding partners also persistently activates CaMKII. A longstanding model invokes two distinct S- and T-sites. If an interactor binds at the T-site, it will preclude autoinhibition and allow substrates to be phosphorylated at the S-site. Here, we specifically test this model with X-ray crystallography, molecular dynamics simulations, and biochemistry. Our data are inconsistent with this model. Co-crystal structures of four different activators or substrates show that they all bind to a single continuous site across the kinase domain. We propose a mechanistic model that persistent CaMKII activity is facilitated by high affinity binding partners, which kinetically compete with autoinhibition by the regulatory segment to allow substrate phosphorylation.

中文翻译：

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CaMKII 在活性位点结合底物和激活剂

Ca ²⁺ /钙调蛋白依赖性蛋白激酶 II (CaMKII) 是长期记忆所需的信号蛋白。^{一旦被 Ca 2+} /CaM激活，即使在 Ca ²⁺消散。除了众所周知的自磷酸化介导机制外，与特定结合伙伴的相互作用也持续激活 CaMKII。一个长期存在的模型调用两个不同的 S 和 T 站点。如果相互作用物在 T 位点结合，它将排除自身抑制并允许底物在 S 位点被磷酸化。在这里，我们专门用 X 射线晶体学、分子动力学模拟和生物化学来测试这个模型。我们的数据与该模型不一致。四种不同激活剂或底物的共晶结构表明它们都与激酶结构域的单个连续位点结合。我们提出了一个机制模型，即持久的 CaMKII 活性由高亲和力结合伙伴促进，