Structures of parasitic CDPK domains point to a common mechanism of activation

Area of Science:

• Structural biology
• Molecular signaling
• Parasitology

Background:

• Calcium-dependent protein kinases (CDPKs) are crucial regulators of cellular processes.
• Apicomplexa, a phylum of parasitic protozoa, possess CDPKs with unique structural and functional properties.
• Previous studies identified novel CDPK structures and activation mechanisms in Apicomplexa.

Purpose of the Study:

• To investigate the universality of a novel calcium-activation mechanism in CDPKs from Apicomplexa.
• To elucidate the structural basis of calcium signaling in these organisms.
• To identify conserved residues and intermediate conformations involved in CDPK activation.

Main Methods:

• X-ray crystallography to determine CDPK structures.
• Comparative sequence and structural analysis across different species.
• Biochemical assays to study calcium binding and conformational changes.

Main Results:

• Determined structures of inactivated and calcium-activated CDPKs from Apicomplexa, revealing a novel EF-hand fold (CDPK activation domain - CAD).
• Identified conserved sequence and structural similarities between apicomplexan and plant CDPKs, suggesting a universal activation mechanism.
• Captured intermediate conformations providing detailed steps in calcium activation and highlighting conserved residues critical for the conformational change.

Conclusions:

• The novel calcium-binding and activation mechanism is likely conserved across canonical CDPKs, particularly within Apicomplexa.
• Specific regulatory elements of inactive and active CDPK forms require further investigation.
• Structural insights into CDPK activation provide a foundation for understanding calcium signaling in parasitic protozoa.