Calmodulin is a small calcium-binding protein that mediates many of the effects of intracellular calcium. When calcium binds to calmodulin, which of the following changes occurs?
- A Calmodulin undergoes autophosphorylation on tyrosine residues
- B Calcium-bound calmodulin undergoes a conformational change that allows it to bind and activate target enzymes ✓
- C Calmodulin hydrolyzes GTP to GDP, inactivating G proteins
- D Calmodulin translocates to the nucleus and acts as a transcription factor
Correct answer: B. Calcium-bound calmodulin undergoes a conformational change that allows it to bind and activate target enzymes
Explanation
Calmodulin contains four EF-hand motifs that bind calcium. Upon calcium binding, calmodulin undergoes a major conformational change, exposing a hydrophobic surface that interacts with and activates numerous target proteins, including calcium-calmodulin-dependent kinases (CaMKs), calcineurin, and myosin light chain kinase. Calmodulin itself has no kinase, GTPase, or transcriptional activity.
Reference: Lehninger Principles of Biochemistry, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.