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Calmodulin-binding sites on adenylyl cyclase type VIII
1Neuroscience Program and Department of Pharmacology, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
The Journal of Biological Chemistry
|March 13, 1999
Summary
Calcium (Ca2+) stimulation of adenylyl cyclase type VIII (ACVIII) involves calmodulin binding at two sites. The C-terminal site is primarily responsible for Ca2+ activation, suggesting a disinhibition mechanism for ACVIII regulation.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- Adenylyl cyclase type VIII (ACVIII) activity is regulated by calcium (Ca2+) through calmodulin.
- The precise binding locations and activation mechanisms of calmodulin on ACVIII remain unelucidated.
Purpose of the Study:
- To identify and characterize the calmodulin-binding sites on ACVIII.
- To elucidate the role of these sites in Ca2+-dependent ACVIII activation.
Main Methods:
- Overlay assays to identify N-terminal binding.
- Mutagenesis studies to investigate C-terminal binding.
- Synthetic peptide studies for site confirmation.
- Functional assays to assess enzyme activity.
Main Results:
- Two calmodulin-binding sites were identified: one at the N terminus and another at the C terminus.
- The N-terminal site exhibits a typical Ca2+-dependent calmodulin-binding motif and may be involved in calmodulin trapping.
- The C-terminal site, resembling an IQ motif, is the primary Ca2+-dependent calmodulin-binding site responsible for ACVIII stimulation.
- Deletion of the C-terminal site leads to a hyperactivated, Ca2+-insensitive ACVIII.
Conclusions:
- Ca2+/calmodulin regulation of ACVIII occurs via two distinct binding sites.
- The C-terminal site mediates Ca2+ stimulation through a likely disinhibitory mechanism.
- ACVIII regulation by Ca2+/calmodulin involves a combination of binding and potential disinhibition.