title: RC3/Neurogranin and Ca2+/calmodulin-dependent protein kinase II produce opposing effects on the affinity of calmodulin for calcium.
abstract: The interaction of calmodulin with its target proteins is known to affect the kinetics and affinity of Ca(2+) binding to calmodulin. Based on thermodynamic principles, proteins that bind to Ca(2+)-calmodulin should increase the affinity of calmodulin for Ca(2+), while proteins that bind to apo-calmodulin should decrease its affinity for Ca(2+). We quantified the effects on Ca(2+)-calmodulin interaction of two neuronal calmodulin targets: RC3, which binds both Ca(2+)- and apo-calmodulin, and alphaCaM kinase II, which binds selectively to Ca(2+)-calmodulin. RC3 was found to decrease the affinity of calmodulin for Ca(2+), whereas CaM kinase II increases the calmodulin affinity for Ca(2+). Specifically, RC3 increases the rate of Ca(2+) dissociation from the C-terminal sites of calmodulin up to 60-fold while having little effect on the rate of Ca(2+) association. Conversely, CaM kinase II decreases the rates of dissociation of Ca(2+) from both lobes of calmodulin and autophosphorylation of CaM kinase II at Thr(286) induces a further decrease in the rates of Ca(2+) dissociation. RC3 dampens the effects of CaM kinase II on Ca(2+) dissociation by increasing the rate of dissociation from the C-terminal lobe of calmodulin when in the presence of CaM kinase II. This effect is not seen with phosphorylated CaM kinase II. The results are interpreted according to a kinetic scheme in which there are competing pathways for dissociation of the Ca(2+)-calmodulin target complex. This work indicates that the Ca(2+) binding properties of calmodulin are highly regulated and reveals a role for RC3 in accelerating the dissociation of Ca(2+)-calmodulin target complexes at the end of a Ca(2+) signal.
authors.affiliation: Department of Neurobiology and Anatomy, University of Texas Medical School, Houston, Texas 77030, USA.
authors.forename: Tara R
authors.initials: TR
authors.lastname: Gaertner
authors.forename: John A
authors.initials: JA
authors.lastname: Putkey
authors.forename: M Neal
authors.initials: MN
authors.lastname: Waxham
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D051579:Neurogranin; D010766:Phosphorylation; D011485:Protein Binding / Q000502:physiology; D051381:Rats; D012617:Sea Urchins
chemical_list: D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D009419:Nerve Tissue Proteins; C496651:Nrgn protein, rat; D051579:Neurogranin; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002118:Calcium