PDBsum entry 2ksz

Metal binding protein

PDB id: 2ksz

Contents

Protein chain

76 a.a. *

Metals

_MG ×2

* Residue conservation analysis

PDB id:

2ksz

Name:

Metal binding protein

Title:

The solution structure of the magnesium bound soybean calmodulin isoform 4 n-domain

Structure:

Putative uncharacterized protein. Chain: a. Fragment: scam4 n-terminal domain. Synonym: scam4-nt, calmodulin. Engineered: yes

Source:

Glycine max. Soybeans. Organism_taxid: 3847. Gene: scam-4. Expressed in: escherichia coli. Expression_system_taxid: 562.

NMR struc:

5 models

Authors:

H.Huang,H.Ishida,H.J.Vogel

Key ref:

H.Huang et al. (2010). 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. PubMed id: 20054830

Date:

14-Jan-10 Release date: 09-Mar-10

Protein chain

Q39890  (Q39890_SOYBN) -  Calmodulin from Glycine max

Seq: 150 a.a.

Struc: 76 a.a.

Protein Sci 19:475-485 (2010)

PubMed id: 20054830

The solution structure of the Mg2+ form of soybean calmodulin isoform 4 reveals unique features of plant calmodulins in resting cells.

H.Huang, H.Ishida, H.J.Vogel.

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.