Indiana University-Purdue University Indianapolis (IUPUI) / Calcium/calmodulin (CaM)-dependent protein kinase II (CaMKII) is a multimeric
holoenzyme composed of 8–14 subunits from four closely related isoforms (α, β, γ, δ).
CaMKII plays a strategic, multifunctional role in coupling the universal second messenger
calcium with diverse cellular processes including metabolism, cell cycle control, and
synaptic plasticity. CaMKII exhibits broad substrate specificity, targeting numerous
substrates with diverse phosphorylation motifs. Binding of the calcium sensor CaM to the
autoregulatory domain (ARD) of CaMKII functions to couple kinase activation with calcium signaling. Important sites of autophosphorylation, namely T287 and T306/7 (δ
isoform numbering), reside within the ARD and control either CaM dependence or ability
to bind to CaMKII respectively, thus determining various activation states of the kinase.
Because autophosphorylation is critical to the function of CaMKII in vivo, we sought to
determine the relationship between the activation state of the kinase and substrate
selectivity. We show that the ARD of activated CaMKII tunes substrate selectivity by
competing for substrate binding to the catalytic domain, thus functioning as a selectivity filter. Specifically, in the absence of T287 autophosphorylation, substrate phosphorylation is limited to high-affinity, consensus substrates. T287 autophosphorylation restores maximal
kinase activation and broad substrate selectivity by disengaging ARD filtering. The unique
multimeric architecture of CaMKII is an ideal sensor which encodes calcium-spike
frequency into graded levels of subunit activation/autophosphorylation within the
holoenzyme. We find that differential activation states of the holoenzyme produce distinct substrate phosphorylation profiles. Maximal holoenzyme activation/autophosphorylation
leads to further broadening of substrate specificity beyond the effect of
autophosphorylation alone, which is consistent with multivalent avidity. Thus, the ability of calcium-spike frequency to regulate T287 autophosphorylation and holoenzyme
activation permits cellular activity to dictate switch-like behavior in substrate selectivity
that is required for diverse cellular responses by CaMKII.
| Identifer | oai:union.ndltd.org:IUPUI/oai:scholarworks.iupui.edu:1805/11291 |
| Date | 06 July 2016 |
| Creators | Johnson, Derrick Ethan |
| Contributors | Hudmon, Andy, Hurley, Thomas D., Hoang, Quyen Q., Gallagher, Patricia |
| Source Sets | Indiana University-Purdue University Indianapolis |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
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