Structural studies of soybean calmodulin isoform 4 bound to the calmodulin-binding domain of tobacco mitogen-activated protein kinase phosphatase-1 provide insights into a sequential target binding mode.
The calcium regulatory protein calmodulin (CaM) binds in a calcium-dependent manner to numerous target proteins. The calmodulin-binding domain (CaMBD) region of Nicotiana tabacum MAPK phosphatase has an amino acid sequence that does not resemble the CaMBD of any other known Ca(2+)-CaM-binding proteins. Using a unique fusion protein strategy, we have been able to obtain a high resolution solution structure of the complex of soybean Ca(2+)-CaM4 (SCaM4) and this CaMBD. Complete isotope labeling of both parts of the complex in the fusion protein greatly facilitated the structure determination by NMR. The 12-residue CaMBD region was found to bind exclusively to the C-lobe of SCaM4. A specific Trp and Leu side chain are utilized to facilitate strong binding through a novel "double anchor" motif. Moreover, the orientation of the helical peptide on the surface of Ca(2+)-SCaM4 is distinct from other known complexes. The N-lobe of Ca(2+)-SCaM4 in the complex remains free for additional interactions and could possibly act as a calcium-dependent adapter protein. Signaling through the MAPK pathway and increases in intracellular Ca(2+) are both hallmarks of the plant stress response, and our data support the notion that coordination of these responses may occur through the formation of a unique CaM-MAPK phosphatase multiprotein complex.
Ishida
Hiroaki
H
Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
Rainaldi
Mario
M
Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
Vogel
Hans J
HJ
Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada. Electronic address: vogel@ucalgary.ca.
D000595:Amino Acid Sequence; D000818:Animals; D002147:Calmodulin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D054638:Dual Specificity Phosphatase 1 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism; D010455:Peptides / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013025:Glycine max / Q000378:metabolism*; D014026:Nicotiana / Q000378:metabolism*
D002147:Calmodulin; D046912:Multiprotein Complexes; D010455:Peptides; D010940:Plant Proteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D054638:Dual Specificity Phosphatase 1