Synaptic frequency decoding by the CaMKII holoenzyme
Higher brain functions are thought to require synaptic frequency decoding that can lead to long-term potentiation (LTP) or depression (LTD). We show that the LTP- versus LTD-decision is determined by complex cross-regulation of T286 and T305/306 autophosphorylation within the 12meric CaMKII holoenzyme, which enabled molecular computation of stimulus frequency, amplitude, and duration. Both LTP and LTD require T286 phosphorylation, but T305/306 phosphorylation selectively promoted LTD. In response to excitatory LTP versus LTD stimuli, the differential T305/306 phosphorylation also directed CaMKII movement to either excitatory or inhibitory synapses, thereby coordinating plasticity at both synapse types. Fast T305/306 phosphorylation required prior T286 phosphorylation and then curbed CaMKII activity by two mechanisms: (i) a cis-subunit reaction reduced both Ca2+-stimulation and autonomous activity, and (ii) a trans-subunit reaction enabled complete activity shut-down and feed-forward inhibition of further T286 phosphorylation. These are surprising fundamental additions to the long-studied CaMKII regulation and function in neuronal plasticity.