Multiple CaMKII Binding Modes to the Actin Cytoskeleton Revealed by Single-Molecule Imaging

Area of Science:

• Neuroscience
• Molecular Biology
• Cell Biology

Background:

• Dendritic spine synapse localization of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is crucial for synaptic plasticity.
• The actin cytoskeleton is known to play a role in CaMKII synaptic targeting, but the direct interactions are not fully understood.

Purpose of the Study:

• To investigate the direct binding interactions between CaMKII and the actin cytoskeleton.
• To determine how CaMKII isoforms and regulatory states affect F-actin binding and synaptic localization.

Main Methods:

• Utilized total internal reflection fluorescence microscopy and single-molecule tracking in live cells.
• Employed stepwise photobleaching and photoactivation experiments to analyze CaMKII-actin interactions.
• Investigated the effects of latrunculin treatment and specific CaMKII mutations on F-actin binding.

Main Results:

• CaMKII forms oligomeric complexes that bind to the F-actin cytoskeleton.
• CaMKIIα isoform binds F-actin, albeit weaker than CaMKIIβ, and this binding is abolished by autophosphorylation-mimicking mutations (αT286D).
• F-actin binding is independent of CaMKII's interaction with GluN2B, ATP, or Ca(2+)/calmodulin.

Conclusions:

• Transient F-actin binding contributes to the synaptic localization of the CaMKIIα isoform.
• Autophosphorylation of CaMKII disrupts F-actin binding, providing a mechanism for reduced synaptic localization of mutants like αT286D.
• CaMKII likely engages in multiple F-actin binding modes, stabilized by contacts between the CaMKII dodecamer and the actin cytoskeleton.