Abstract
CaMKII (Ca²⁺/calmodulin-dependent protein kinase II) is a multifunctional enzyme essential for synaptic plasticity, learning, and memory. It is highly enriched within the postsynaptic density (PSD), where its activation and localization are tightly linked to synaptic activity, playing a critical role in processes such as NMDA (N-methyl-d-aspartate) receptor (NMDAR)-dependent long-term potentiation (LTP). The induction of LTP requires CaMKII localization to the synapse via interaction with NMDARs, while its maintenance relies on activation-dependent local translation of CaMKII at the synapse, underscoring its pivotal role in sustaining synaptic function. While these mechanisms of activation, localization, and translation are well characterized, how the proteostasis of such a synaptically enriched protein is maintained remains poorly understood. This gap in understanding drives the need to investigate the mechanisms regulating CaMKII degradation. This study aimed to elucidate the factors influencing CaMKII degradation and their broader regulatory implications. To address this, a combination of biochemical assays, pulse-chase experiments using SNAP-tag technology, and mutagenesis was employed to assess how activation state, oligomerization state, and subunit exchange contribute to CaMKII degradation. Constructs representing distinct activation and oligomerization states were analyzed, along with chimeric proteins derived from Rattus Norvegicus and Drosophila Melanogaster CaMKII homologs, to identify both conserved and species-specific regulatory mechanisms. The findings revealed that neither subunit exchange nor oligomerization state serves as the primary determinant of degradation. Instead, autonomous activation was identified as the critical factor driving CaMKII degradation. Further evidence implicated the ubiquitin-proteasome system (UPS) as the likely pathway responsible for this process. Comparative analysis showed that activation-dependent degradation is conserved across species but occurs more rapidly in Rattus Norvegicus CaMKII (rCaMKll) within HEK293T cells, a difference attributed to non-conserved regulatory elements within the catalytic, regulatory, and linker domains. These results identify autonomous activation as the key determinant of CaMKII degradation and highlight a conserved mechanism that may regulate synaptic protein turnover. Additionally, the identification of species-specific regulatory determinants provides new insights into the structural and functional evolution of CaMKII. Together, these findings enhance our understanding of CaMKll homeostasis and provide insight into how neuronal signaling integrity may be preserved.