Heterogeneity in human hippocampal CaMKII transcripts reveals allosteric hub-dependent regulation

Ca 2+ -calmodulin dependent protein kinase II (CaMKII) plays a central role in Ca 2+ signaling throughout the body. Specifically in the hippocampus, CaMKII is required for learning and memory. CaMKII is encoded by four highly conserved genes in vertebrates: α, β, γ, and δ. AllCaMKIIs are comprised of a kinase domain, regulatory segment, variable linker region, and hub domain responsible for oligomerization. The four genes differ primarily in linker length and composition due to extensive alternative splicing. Here, we unambiguously report the heterogeneity of CaMKII transcripts in 3 complex samples of human hippocampus using Illumina sequencing. Our results show that hippocampal cells contain a diverse collection of 70 CaMKII transcripts from all four CaMKII genes. We characterized the Ca 2+ /CaM sensitivity of hippocampal CaMKII variants spanning a broad range of linker lengths and compositions. We demonstrate that the effect of the variable linker on Ca 2+ /CaM sensitivity is conditional on kinase and hub domains. Moreover, we reveal a novel role for the hub domain as an allosteric regulator of kinase activity, which may provide a new pharmacological target for modulating CaMKII activity. Using small angle X-ray scattering and single-particle electron cryo-microscopy, we present evidence for extensive interaction between the kinase and the hub domain, even in the presence of a 30-residue linker. Taken together, we propose that Ca 2+ /CaM sensitivity in CaMKII is gene-dependent and includes significant contributions from the hub. Our sequencing approach combined with biochemistry provides new insights into understanding the complex pool of endogenous CaMKII. One Sentence Summary CaMKII is a well-conserved protein that is essential for learning and memory. When CaMKII is mutated in a mouse, this mouse has difficulty learning and remembering how to get through a maze. The hippocampus is the part of the brain required for memory. Here, we used a specific experiment to determine every type of CaMKII that is in a human hippocampus. We found 70 different types and then asked how these differences affect CaMKII function. These data provide evidence that an assembly domain of CaMKII plays an unexpected role regulating its activity. This new finding helps us better understand endogenous CaMKII in the brain and provides a new mechanism for modulating CaMKII activity.