2KSZ

The solution structure of the Magnesium bound soybean calmodulin isoform 4 N-domain

Summary for 2KSZ

• Entry DOI: 10.2210/pdb2ksz/pdb
• Related: 1F70 2ROA
• Descriptor: Putative uncharacterized protein, MAGNESIUM ION (2 entities in total)
• Functional Keywords: soybean calmodulin isoform 4, magnesium, residual dipolar coupling, metal binding protein
• Biological source: Glycine max (soybeans)
• Total number of polymer chains: 1
• Total formula weight: 8482.86

Authors

Huang, H.,Ishida, H.,Vogel, H.J. (deposition date: 2010-01-14, release date: 2010-03-09, Last modification date: 2024-05-01)

Primary citation

Huang, H.,Ishida, H.,Vogel, H.J.
The solution structure of the Mg2+ form of soybean calmodulin isoform 4 reveals unique features of plant calmodulins in resting cells.
Protein Sci., 19:475-485, 2010

PubMed Abstract: 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. Because of the fact that free Mg(2+) ions are always present at high concentrations in cells (0.5-2 mM), we suggest that Mg(2+) should be bound to sCaM4 in nonactivated 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 restraints (1)D(NH), (1)D(C alpha H alpha), and (1)D(C'C alpha) 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 and 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.

PubMed: 20054830
DOI: 10.1002/pro.325

Experimental method

SOLUTION NMR