The CaMKII holoenzyme structure in activation-competent conformations

Area of Science:

• Neuroscience
• Structural Biology
• Biochemistry

Background:

• Calcium/calmodulin-dependent protein kinase II (CaMKII) is essential for synaptic plasticity, learning, and memory.
• CaMKII functions as a large 12-meric holoenzyme, but its structural dynamics and conformational states remain incompletely understood.

Purpose of the Study:

• To determine the pseudoatomic structure of the CaMKIIα holoenzyme in an activation-competent conformation.
• To investigate the dynamic range and conformational plasticity of the CaMKII holoenzyme.

Main Methods:

• Single particle electron microscopy (EM) to generate a pseudoatomic model.
• Biochemical assays and Förster resonance energy transfer (FRET) studies.

Main Results:

• A pseudoatomic model of an extended, activation-competent CaMKIIα holoenzyme was determined.
• The holoenzyme exhibits significant flexibility in kinase domain positioning, with diameters ranging from 15-35 nm.
• A small fraction of 14-mers was observed, suggesting potential subunit exchange mechanisms.

Conclusions:

• The extended conformation is the predominant state of CaMKIIα, even under molecular crowding.
• The structural plasticity of CaMKII holoenzymes is critical for their role in synaptic plasticity and cognitive functions.