title: Dual effect of ATP in the activation mechanism of brain Ca(2+)/calmodulin-dependent protein kinase II by Ca(2+)/calmodulin.
abstract: The activation mechanism of Ca(2+)/calmodulin-dependent protein kinase II (alphaCaMKII) is investigated by steady-state and stopped-flow fluorescence spectroscopies. Lys(75)-labeled TA-cal [Török, K., and Trentham, D. R. (1994) Biochemistry 33, 12807-12820] is used to measure binding events, and double-labeled AEDANS,DDP-T34C/T110/C-calmodulin [Drum et al. (2000) J. Biol. Chem. 275, 36334-36340] (DA-cal) is used to detect changes in calmodulin conformation. Fluorescence quenching of DA-cal attributed to resonance energy transfer is related to the compactness of the calmodulin molecule. Interprobe distances are estimated by lifetime measurements of Ca(2+)/DA-cal in complexes with unphosphorylated nucleotide-free, nucleotide-bound, and Thr(286)-phospho-alphaCaMKII as well as with alphaCaMKII-derived calmodulin-binding peptides in the presence of Ca(2+). These measurements show that calmodulin can assume at least two spectrally distinct conformations when bound to alphaCaMKII with estimated interprobe distances of 40 and 22-26 A. Incubation with ATP facilitates the assumption of the most compact conformation. Nonhydrolyzable ATP analogues partially replicate the effects of ATP, suggesting that while the binding of ATP induces a conformational change, Thr(286)-autophosphorylation is probably required for the transition of calmodulin into its most compact conformer. The rate constant for the association of Ca(2+)/TA-cal with alphaCaMKII is estimated as 2 x 10(7) M(-1) s(-1) and is not substantially affected by the presence of ATP. The rate of net calmodulin compaction measured by Ca(2+)/DA-cal is markedly slower, occurring with a rate constant of 2.5 x 10(6) M(-1) s(-1), suggesting that unproductive complexes may play a role in the activation mechanism.
authors.affiliation: Department of Pharmacology and Clinical Pharmacology, St. George's Hospital Medical School, London SW17 0RE, U.K. k.torok@sghms.ac.uk
authors.forename: K
authors.initials: K
authors.lastname: Török
authors.forename: A
authors.initials: A
authors.lastname: Tzortzopoulos
authors.forename: Z
authors.initials: Z
authors.lastname: Grabarek
authors.forename: S L
authors.initials: SL
authors.lastname: Best
authors.forename: R
authors.initials: R
authors.lastname: Thorogate
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D004735:Energy Transfer; D004789:Enzyme Activation; D006801:Humans; D008024:Ligands; D011485:Protein Binding; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence
chemical_list: D002147:Calmodulin; D008024:Ligands; D000255:Adenosine Triphosphate; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002118:Calcium