Energetics of target peptide binding by calmodulin reveals different modes of binding.
Thermodynamic parameters of interactions of calcium-saturated calmodulin (Ca(2+)-CaM) with melittin, C-terminal fragment of melittin, or peptides derived from the CaM binding regions of constitutive (cerebellar) nitric-oxide synthase, cyclic nucleotide phosphodiesterase, calmodulin-dependent protein kinase I, and caldesmon (CaD-A, CaD-A*) have been measured using isothermal titration calorimetry. The peptides could be separated into two groups according to the change in heat capacity upon complex formation, DeltaC(p). The calmodulin-dependent protein kinase I, constitutive (cerebellar) nitric-oxide synthase, and melittin peptides have DeltaC(p) values clustered around -3.2 kJ.mol(-1).K(-1), consistent with the formation of a globular CaM-peptide complex in the canonical fashion. In contrast, phosphodiesterase, the C-terminal fragment of melittin, CaD-A, and CaD-A* have DeltaC(p) values clustered around -1.6 kJ.mol(-1).K(-1), indicative of interactions between the peptide and mostly one lobe of CaM, probably the C-terminal lobe. It is also shown that the interactions for different peptides with Ca(2+)-CaM can be either enthalpically or entropically driven. The difference in the energetics of peptide/Ca(2+)-CaM complex formation appears to be due to the coupling of peptide/Ca(2+)-CaM complex formation to the coil-helix transition of the peptide. The binding of a helical peptide to Ca(2+)-CaM is dominated by favorable entropic effects, which are probably mostly due to hydrophobic interactions between nonpolar groups of the peptide and Ca(2+)-CaM. Applications of these findings to the design of potential CaM inhibitors are discussed.
Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
R D
RD
Brokx
M M
MM
Lopez
H J
HJ
Vogel
G I
GI
Makhatadze
D000595:Amino Acid Sequence; D000818:Animals; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism*; D002151:Calorimetry / Q000379:methods; D019277:Entropy; D004926:Escherichia coli / Q000378:metabolism; D006358:Hot Temperature; D007700:Kinetics; D008555:Melitten / Q000737:chemistry; D008745:Methylation; D008969:Molecular Sequence Data; D010455:Peptides / Q000378:metabolism*; D010727:Phosphoric Diester Hydrolases / Q000737:chemistry; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D013696:Temperature; D013816:Thermodynamics
D002147:Calmodulin; D010455:Peptides; D008555:Melitten; D010727:Phosphoric Diester Hydrolases