PDBsum entry 1sbj

Contractile protein, structural protein

PDB id: 1sbj

Contents

Protein chain

81 a.a. *

Metals

_MG ×2

* Residue conservation analysis

PDB id:

1sbj

Name:

Contractile protein, structural protein

Title:

Nmr structure of the mg2+-loaded c terminal domain of cardiac troponin c bound to the n terminal domain of cardiac troponin i

Structure:

Troponin c, slow skeletal and cardiac muscles. Chain: a. Fragment: c-terminal domain (residues 81 - 161). Synonym: tn-c. Engineered: yes

Source:

Gallus gallus. Chicken. Organism_taxid: 9031. Gene: ctnc. Expressed in: escherichia coli bl21(de3). Expression_system_taxid: 469008.

NMR struc:

20 models

Authors:

N.L.Finley,J.W.Howarth,P.R.Rosevear

Key ref:

N.L.Finley et al. (2004). Structure of the Mg2+-loaded C-lobe of cardiac troponin C bound to the N-domain of cardiac troponin I: comparison with the Ca2+-loaded structure. Biochemistry, 43, 11371-11379. PubMed id: 15350124 DOI: 10.1021/bi049672i

Date:

10-Feb-04 Release date: 23-Nov-04

Protein chain

P09860  (TNNC1_CHICK) -  Troponin C, slow skeletal and cardiac muscles from Gallus gallus

Seq: 161 a.a.

Struc: 81 a.a.

DOI no: 10.1021/bi049672i

Biochemistry 43:11371-11379 (2004)

PubMed id: 15350124

Structure of the Mg2+-loaded C-lobe of cardiac troponin C bound to the N-domain of cardiac troponin I: comparison with the Ca2+-loaded structure.

N.L.Finley, J.W.Howarth, P.R.Rosevear.

ABSTRACT

Cardiac troponin C (cTnC) is the Ca(2+)-binding component of the troponin complex and, as such, is the Ca(2+)-dependent switch in muscle contraction. This protein consists of two globular lobes, each containing a pair of EF-hand metal-binding sites, connected by a linker. In the N lobe, Ca(2+)-binding site I is inactive and Ca(2+)-binding site II is primarily responsible for initiation of muscle contraction. The C lobe contains Ca(2+)/Mg(2+)-binding sites III and IV, which bind Mg(2+) with lower affinity and play a structural as well as a secondary role in modulating the Ca(2+) signal. To understand the structural consequences of Ca(2+)/Mg(2+) exchange in the C lobe, we have determined the NMR solution structure of the Mg(2+)-loaded C lobe, cTnC(81-161), in a complex with the N domain of cardiac troponin I, cTnI(33-80), and compared it with a refined Ca(2+)-loaded structure. The overall tertiary structure of the Mg(2+)-loaded C lobe is very similar to that of the refined Ca(2+)-loaded structure as evidenced by the root-mean-square deviation of 0.94 A for all backbone atoms. While metal-dependent conformational changes are minimal, substitution of Mg(2+) for Ca(2+) is characterized by condensation of the C-terminal portion of the metal-binding loops with monodentate Mg(2+) ligation by the conserved Glu at position 12 and partial closure of the cTnI hydrophobic binding cleft around site IV. Thus, conformational plasticity in the Ca(2+)/Mg(2+)-dependent binding loops may represent a mechanism to modulate C-lobe cTnC interactions with the N domain of cTnI.