title: Kinetic and mechanistic differences in the interactions between caldendrin and calmodulin with AKAP79 suggest different roles in synaptic function.
abstract: The kinetic and mechanistic details of the interaction between caldendrin, calmodulin and the B-domain of AKAP79 were determined using a biosensor-based approach. Caldendrin was found to compete with calmodulin for binding at AKAP79, indicating overlapping binding sites. Although the AKAP79 affinities were similar for caldendrin (K(D) = 20 nM) and calmodulin (K(D) = 30 nM), their interaction characteristics were different. The calmodulin interaction was well described by a reversible one-step model, but was only detected in the presence of Ca(2+). Caldendrin interacted with a higher level of complexity, deduced to be an induced fit mechanism with a slow relaxation back to the initial encounter complex. It interacted with AKAP79 also in the absence of Ca(2+), but with different kinetic rate constants. The data are consistent with a similar initial Ca(2+)-dependent binding step for the two proteins. For caldendrin, a second Ca(2+)-independent rearrangement step follows, resulting in a stable complex. The study shows the importance of establishing the mechanism and kinetics of protein-protein interactions and that minor differences in the interaction of two homologous proteins can have major implications in their functional characteristics. These results are important for the further elucidation of the roles of caldendrin and calmodulin in synaptic function.
authors.affiliation: Beactica AB, Uppsala, Sweden.
authors.forename: Christian
authors.initials: C
authors.lastname: Seeger
authors.forename: Xenia
authors.initials: X
authors.lastname: Gorny
authors.forename: Pasham Parameshwar
authors.initials: PP
authors.lastname: Reddy
authors.forename: Constanze
authors.initials: C
authors.lastname: Seidenbecher
authors.forename: U Helena
authors.initials: UH
authors.lastname: Danielson
mesh_terms: D054758:A Kinase Anchor Proteins / Q000737:chemistry*; D001665:Binding Sites; D001667:Binding, Competitive; D001923:Brain Chemistry; D002118:Calcium / Q000737:chemistry*; D002135:Calcium-Binding Proteins / Q000737:chemistry*; D002147:Calmodulin / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D012996:Solutions; D020349:Surface Plasmon Resonance; D013569:Synapses / Q000737:chemistry / Q000378:metabolism
chemical_list: D054758:A Kinase Anchor Proteins; C487775:AKAP5 protein, human; D002135:Calcium-Binding Proteins; D002147:Calmodulin; D011993:Recombinant Fusion Proteins; D012996:Solutions; C085577:Ca2+-binding protein-1; D002118:Calcium