Covert Changes in CaMKII Holoenzyme Structure Identified for Activation and Subsequent Interactions

Area of Science:

• Molecular Biology
• Neuroscience
• Biochemistry

Background:

• Calcium-calmodulin dependent protein kinase-II (CaMKII) is crucial for synaptic activity.
• CaMKII holoenzymes exist as complexes of 8-14 subunits organized around a central core.
• The functional role of catalytic-domain pairing in CaMKII activity remains unclear.

Purpose of the Study:

• To investigate the structural rearrangements of CaMKII holoenzymes during activation.
• To test the hypothesis that catalytic-domain pairing regulates kinase activity by controlling ATP access.
• To explore the role of Threonine-286 interaction sites (T-sites) in CaMKII function.

Main Methods:

• Utilized simultaneous homo-FRET and fluorescence correlation spectroscopy in living cells.
• Measured structural changes correlated with kinase activation under physiological conditions.
• Employed site-directed mutagenesis (I205K) to probe T-site function.

Main Results:

• Ca(2+)/CaM activation induced Threonine-286 autophosphorylation and increased holoenzyme hydrodynamic volume.
• No significant change in catalytic-domain pair proximity or subunit stoichiometry was observed upon activation.
• T-site ligand addition decreased catalytic-domain homo-FRET, indicating altered pairing, an effect blocked by I205K mutation.

Conclusions:

• Catalytic-domain pairing does not prevent ATP access but is altered to facilitate T-site interactions.
• This structural rearrangement is essential for CaMKII holoenzyme interactions with target proteins.
• Findings provide a new model for CaMKII regulation and function in synaptic plasticity.