title: Structurally homologous binding of plant calmodulin isoforms to the calmodulin-binding domain of vacuolar calcium-ATPase.
abstract: The discovery that plants contain multiple calmodulin (CaM) isoforms having variable sequence identity to mammalian CaM has sparked a flurry of new questions regarding the intracellular role of Ca(2+) regulation in plants. To date, the majority of research in this field has focused on the differential enzymatic regulation of various mammalian CaM-dependent enzymes by the different plant CaM isoforms. However, there is comparatively little information on the structural recognition of target enzymes found exclusively in plant cells. Here we have used a variety of spectroscopic techniques, including nuclear magnetic resonance, circular dichroism, and fluorescence spectroscopy, to study the interactions of the most conserved and most divergent CaM isoforms from soybean, SCaM-1, and SCaM-4, respectively, with a synthetic peptide derived from the CaM-binding domain of cauliflower vacuolar calcium-ATPase. Despite their sequence divergence, both SCaM-1 and SCaM-4 interact with the calcium-ATPase peptide in a similar calcium-dependent, stoichiometric manner, adopting an antiparallel binding orientation with an alpha-helical peptide. The single Trp residue is bound in a solvent-inaccessible hydrophobic pocket on the C-terminal domain of either protein. Thermodynamic analysis of these interactions using isothermal titration calorimetry demonstrates that the formation of each calcium-SCaM-calcium-ATPase peptide complex is driven by favorable binding enthalpy and is very similar to the binding of mammalian CaM to the CaM-binding domains of myosin light chain kinases and calmodulin-dependent protein kinase I.
authors.affiliation: Structural Biology Research Group, Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Aaron P
authors.initials: AP
authors.lastname: Yamniuk
authors.forename: Hans J
authors.initials: HJ
authors.lastname: Vogel
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D001937:Brassica / Q000201:enzymology; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000737:chemistry / Q000378:metabolism*; D002147:Calmodulin / Q000737:chemistry / Q000378:metabolism*; D002942:Circular Dichroism; D017124:Conserved Sequence; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism*; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D013025:Glycine max / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
chemical_list: D002147:Calmodulin; D010446:Peptide Fragments; D020033:Protein Isoforms; D000252:Calcium-Transporting ATPases; D002118:Calcium