A brain-specific Ca2+/calmodulin-dependent protein kinase (CaM kinase-Gr) is regulated by autophosphorylation. Relevance to neuronal Ca2+ signaling.
A neuronal Ca2+/calmodulin-dependent protein kinase (CaM kinase-Gr) undergoes autophosphorylation on a serine residue(s) in response to Ca2+ and calmodulin. Phosphate incorporation leads to the formation of a Ca(2+)-independent (autonomous) activity state, as well as potentiation of the Ca2+/calmodulin-dependent response. The autonomous enzyme activity of the phosphorylated enzyme approximately equals the Ca2+/calmodulin-stimulated activity of the unphosphorylated enzyme, but displays diminished affinity toward ATP and the synthetic substrate, syntide-2. The Km(app) for ATP and syntide-2 increased 4.3- and 1.7-fold, respectively. Further activation of the autonomous enzyme by Ca2+/calmodulin yields a marked increase in the affinity for ATP and peptide substrate such that the Km(app) for ATP and syntide-2 decreased by 14- and 8-fold, respectively. Both autophosphorylation and the addition of Ca2+/calmodulin are required to produce the maximum level of enzyme activation and to increase substrate affinity. Unlike Ca2+/calmodulin-dependent protein kinase type II that is dephosphorylated by the Mg(2+)-independent phosphoprotein phosphatases 1 and 2A, CaM kinase-Gr is dephosphorylated by a Mg(2+)-dependent phosphoprotein phosphatase that may be related to the type 2C enzyme. Dephosphorylation of CaM kinase-Gr reverses the effects of autophosphorylation on enzyme activity. A comparison between the autophosphorylation and dephosphorylation reactions of CaM kinase-Gr and Ca2+/calmodulin-dependent protein kinase type II provides useful insights into the operation of Ca(2+)-sensitive molecular switches.
Frangakis
M V
MV
Wellcome Research Laboratories, Research Triangle Park, North Carolina 27709.
Ohmstede
C A
CA
Sahyoun
N
N
D000255:Adenosine Triphosphate / Q000378:metabolism; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001345:Autoradiography; D001921:Brain / Q000201:enzymology*; D002118:Calcium / Q000502:physiology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D006706:Homeostasis; D007700:Kinetics; D008297:Male; D008970:Molecular Weight; D009474:Neurons / Q000201:enzymology / Q000502:physiology*; D010748:Phosphopeptides / Q000302:isolation & purification; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D011487:Protein Conformation; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D015398:Signal Transduction
D000596:Amino Acids; D010748:Phosphopeptides; D010761:Phosphorus Radioisotopes; D000255:Adenosine Triphosphate; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002118:Calcium