The dendritic peptide neurogranin can regulate a calmodulin-dependent target.
Neurogranin, a peptide capable of binding the calcium-poor form of calmodulin, was tested in vitro for its ability to modulate a typical calmodulin target. The target employed was the calcium/calmodulin-dependent form of nitric oxide synthase, which is produced by several different types of neurons. Neurogranin for the study was purified from perchloric acid-soluble calf brain proteins by a combination of calmodulin-Sepharose affinity chromatography and reverse-phase HPLC. The protocol yielded highly purified neurogranin that was active in assays using purified nitric oxide synthase. The titration of the enzyme activity with neurogranin demonstrated a concentration-dependent effect of the peptide on enzyme activation. Subsequent analysis of the ability of increased calcium concentrations to activate the enzyme was performed in the presence of different amounts of neurogranin. The effect of neurogranin on the calcium-dependent activation of the enzyme was to depress enzyme activity in the range of 0.2 to approximately 1 microM calcium. Treatment of the neurogranin peptide with protein kinase C eliminated its inhibition on nitric oxide synthase activation. Treatment of the protein kinase C-phosphorylated peptide with calcineurin did not restore the ability of neurogranin to inhibit enzyme activity, whereas treatment with alkaline phosphatase did restore this ability. These results suggest that neurogranin may serve as a member of a unique class of endogenous calmodulin inhibitor that functions to regulate the activation of calmodulin-requiring targets in neurons.
Martzen
M R
MR
Department of Neurobiology and Anatomy, University of Rochester Medical Center, NY 14642.
Slemmon
J R
JR
D000469:Alkaline Phosphatase / Q000378:metabolism / Q000502:physiology; D000594:Amino Acid Oxidoreductases / Q000378:metabolism / Q000502:physiology; D000818:Animals; D019703:Calcineurin; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000502:physiology*; D002148:Calmodulin-Binding Proteins / Q000032:analysis* / Q000378:metabolism / Q000502:physiology*; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D003712:Dendrites / Q000737:chemistry*; D009419:Nerve Tissue Proteins / Q000032:analysis* / Q000378:metabolism / Q000502:physiology*; D051579:Neurogranin; D019001:Nitric Oxide Synthase; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism / Q000502:physiology
D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D009419:Nerve Tissue Proteins; D051579:Neurogranin; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases; D011493:Protein Kinase C; D000469:Alkaline Phosphatase; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D002118:Calcium