Structural analysis of a calmodulin variant from rice: the C-terminal extension of OsCaM61 regulates its calcium binding and enzyme activation properties.
OsCaM61 is one of five calmodulins known to be present in Oryza sativa that relays the increase of cytosolic [Ca(2+)] to downstream targets. OsCaM61 bears a unique C-terminal extension with a prenylation site. Using nuclear magnetic resonance (NMR) spectroscopy we studied the behavior of the calmodulin (CaM) domain and the C-terminal extension of OsCaM61 in the absence and presence of Ca(2+). NMR dynamics data for OsCaM61 indicate that the two lobes of the CaM domain act together unlike the independent behavior of the lobes seen in mammalian CaM and soybean CaM4. Also, data demonstrate that the positively charged nuclear localization signal region in the tail in apo-OsCaM61 is helical, whereas it becomes flexible in the Ca(2+)-saturated protein. The extra helix in apo-OsCaM61 provides additional interactions in the C-lobe and increases the structural stability of the closed apo conformation. This leads to a decrease in the Ca(2+) binding affinity of EF-hands III and IV in OsCaM61. In Ca(2+)-OsCaM61, the basic nuclear localization signal cluster adopts an extended conformation, exposing the C-terminal extension for prenylation or enabling OsCaM61 to be transferred to the nucleus. Moreover, Ser(172) and Ala(173), residues in the tail, interact with different regions of the protein. These interactions affect the ability of OsCaM61 to activate different target proteins. Altogether, our data show that the tail is not simply a linker between the prenyl group and the protein but that it also provides a new regulatory mechanism that some plants have developed to fine-tune Ca(2+) signaling events.
From the Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada and.
Mostafa
M
Jamshidiha
Hiroaki
H
Ishida
Cindy
C
Sutherland
Jessica L
JL
Gifford
Michael P
MP
Walsh
Hans J
HJ
Vogel
D000818:Animals; D020013:Calcium Signaling / Q000502:physiology*; D002147:Calmodulin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019913:Nuclear Localization Signals; D019906:Nuclear Magnetic Resonance, Biomolecular; D012275:Oryza / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017368:Protein Prenylation / Q000502:physiology*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013025:Glycine max / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D002147:Calmodulin; D019913:Nuclear Localization Signals; D010940:Plant Proteins
Calcium Signaling; Calmodulin; Chemical Shift Perturbations; Dynamics; Enzyme Kinetics; NMR; NMR Titrations; Nuclear Localization Signal; OsCaM61; Protein Dynamics