Calmodulin complexes with brain and muscle creatine kinase peptides.

Area of Science:

• Biochemistry
• Structural Biology
• Cellular Signaling

Background:

• Calmodulin (CaM) is a key calcium (Ca²⁺) sensor regulating cellular processes by binding diverse protein targets.
• Creatine kinase (CK) is crucial for cellular energy homeostasis.
• Understanding CaM-CK interactions provides insights into energy metabolism and signaling pathways.

Purpose of the Study:

• To determine the high-resolution structures of calmodulin in complex with peptides from human brain and muscle creatine kinase.
• To elucidate the binding mode and stoichiometry of CaM-CK peptide interactions.
• To investigate the implications of these interactions for cellular energy regulation and calcium signaling.

Main Methods:

• High-resolution X-ray crystallography (1.24 Å and 1.43 Å).
• Isothermal titration calorimetry (ITC) to confirm stoichiometry.
• Peptide complex structural analysis.

Main Results:

• Two high-resolution X-ray structures of CaM-CK peptide complexes were determined.
• A rare 1:2 CaM:peptide stoichiometry was observed, with each CaM domain binding a peptide independently.
• Distinct peptide binding orientations in the N-terminal domain were identified between brain and muscle CK peptides.
• Ca²⁺-dependent binding was confirmed.

Conclusions:

• The study reveals a novel, extended binding mode of CaM with CK peptides.
• Structural differences in peptide binding suggest potential for distinct regulation of full-length CK isoforms.
• These findings link cellular energy homeostasis with Ca²⁺-mediated signaling, offering insights into cellular energy "fine-tuning".