The solution structure of a plant calmodulin and the CaM-binding domain of the vacuolar calcium-ATPase BCA1 reveals a new binding and activation mechanism.
The type IIb class of plant Ca(2+)-ATPases contains a unique N-terminal extension that encompasses a calmodulin (CaM) binding domain and an auto-inhibitory domain. Binding of Ca(2+)-CaM to this region can release auto-inhibition and activates the calcium pump. Using multidimensional NMR spectroscopy, we have determined the solution structure of the complex of a plant CaM isoform with the CaM-binding domain of the well characterized Ca(2+)-ATPase BCA1 from cauliflower. The complex has a rather elongated structure in which the two lobes of CaM do not contact each other. The anchor residues Trp-23 and Ile-40 form a 1-8-18 interaction motif. Binding of Ca(2+)-CaM gives rise to the induction of two helical parts in this unique target peptide. The two helical portions are connected by a highly positively charged bend region, which represents a relatively fixed angle and positions the two lobes of CaM in an orientation that has not been seen before in any complex structure of calmodulin. The behavior of the complex was further characterized by heteronuclear NMR dynamics measurements of the isotope-labeled protein and peptide. These data suggest a unique calcium-driven activation mechanism for BCA1 and other plant Ca(2+)-ATPases that may also explain the action of calcium-CaM on some other target enzymes. Moreover, CaM activation of plant Ca(2+)-ATPases seems to occur in an organelle-specific manner.
Ishida
Hiroaki
H
Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
Vogel
Hans J
HJ
D020816:Amino Acid Motifs; D001937:Brassica / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002147:Calmodulin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019906:Nuclear Magnetic Resonance, Biomolecular; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010944:Plants; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D014617:Vacuoles / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D002147:Calmodulin; D010940:Plant Proteins; D020033:Protein Isoforms; D000252:Calcium-Transporting ATPases; D002118:Calcium