2ksz

Publication Abstract from PubMed

Soybean calmodulin isoform 4 (sCaM4) is a plant calcium binding protein, regulating cellular responses to the second messenger Ca(2+). We have found that the metal ion free (apo-) form of sCaM4 possesses a half unfolded structure, with the N-terminal domain unfolded and the C-terminal domain folded. This result was unexpected as the apo-forms of both soybean calmodulin isoform 1 (sCaM1) and mammalian CaM (mCaM) are fully folded. Due to the fact that free Mg(2+) ions are always present at high concentrations in cells (0.5 approximately 2 mM), we suggest that Mg(2+) should be bound to sCaM4 in non-activated cells. CD studies revealed that in the presence of Mg(2+) the initially unfolded N-terminal domain of sCaM4 folds into an alpha-helix-rich structure, similar to the Ca(2+)-form. We have used the NMR backbone residual dipolar coupling (RDC) restraints (1)D(NH), (1)D(CalphaHalpha), and (1)D(C)'(Calpha) to determine the solution structure of the N-terminal domain of Mg(2+)-sCaM4 (Mg(2+)-sCaM4-NT). Compared with the known structure of Ca(2+)-sCaM4, the structure of the Mg(2+)-sCaM4-NT does not fully open the hydrophobic pocket, which was further confirmed by the use of the fluorescent probe ANS. Tryptophan fluorescence experiments were used to study the interactions between Mg(2+)-sCaM4 and CaM-binding peptides derived from smooth muscle myosin light chain kinase as well as plant glutamate decarboxylase. These results suggest that Mg(2+)-sCaM4 does not bind to Ca(2+)-CaM target peptides, and therefore is functionally similar to apo-mCaM. The Mg(2+)- and apo- structures of the sCaM4-NT provide unique insights into the structure and function of some plant calmodulins in resting cells.

The solution structure of the Mg(2+)- form of soybean calmodulin isoform 4 reveals unique features of plant calmodulins in resting cells.,Huang H, Ishida H, Vogel HJ Protein Sci. 2010 Jan 6. PMID:20054830^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.