PDBsum entry 1tnx

Calcium-binding protein

PDB id: 1tnx

Contents

Protein chain

145 a.a.

References listed in PDB file

Key reference

Title

Nmr solution structure of calcium-Saturated skeletal muscle troponin c.

Authors

C.M.Slupsky, B.D.Sykes.

Ref.

Biochemistry, 1995, 34, 15953-15964.

PubMed id

8519752

Note In the PDB file this reference is annotated as "TO BE PUBLISHED". The citation details given above were identified by an automated search of PubMed on title and author names, giving a percentage match of 85%.

Abstract

Troponin C (TnC) is an 18 kDa (162-residue) thin-filament calcium-binding protein responsible for triggering muscle contraction upon the release of calcium from the sarcoplasmic reticulum. The structure of TnC with two calcium ions bound has previously been solved by X-ray methods. Shown here is the solution structure of TnC which has been solved using 3D and 4D heteronuclear nuclear magnetic resonance (NMR) spectroscopic techniques. The 1H, 13C, and 15N backbone chemical shifts have already been published [Slupsky, C. M., Reinach, F. C., Smillie, L. B., & Sykes, B. D. (1995) Protein Sci. 4, 1279-1290]. Presented herein are the 1H, 13C, and 15N side-chain chemical shifts which are 80% complete. The structure of calcium-saturated TnC was determined on the basis of 2106 NOE-derived distance restraints, 121 phi dihedral angle restraints, and 76 psi dihedral angle restraints. The appearance of calcium-saturated TnC reveals a dumbbell-shaped molecule with two globular domains connected by a linker. The structures of the N-terminal and C-terminal domains are highly converged [backbone atomic root mean square deviations (rmsd) about the mean atomic coordinate position for residues 10-80 and 98-155 are 0.66 +/- 0.17 and 0.69 +/- 0.18 A, respectively]; however, the orientation of one domain with respect to the other is not well-defined, and thus each domain appears to be structurally independent. Comparison of the calcium-saturated form of TnC determined herein with the half-saturated form determined by X-ray methods reveals two major differences. First, there is a major structural change which occurs in the N-terminal domain resulting in the opening of a hydrophobic pocket presumably to present itself to its target protein troponin I. This structural change appears to involve only helices B and C which move away from helices N/A/D by the alteration of the backbone phi, psi angles of glutamic acid 41 from irregular in the crystal structure (-97 degrees, -7 degrees) to helical in the NMR calcium-saturated structure (-60 degrees, -34 degrees). The other difference between the two structures is the presence of a flexible linker between the two domains in the NMR structure. This flexible linker allows the two domains of TnC to adopt any orientation with respect to one another such that they can interact with a variety of targets.

Secondary reference #1

Title

Solution secondary structure of calcium-Saturated troponin c monomer determined by multidimensional heteronuclear nmr spectroscopy.

Authors

C.M.Slupsky, F.C.Reinach, L.B.Smillie, B.D.Sykes.

Ref.

Protein Sci, 1995, 4, 1279-1290. [DOI no: 10.1002/pro.5560040704]

PubMed id

7670371

Figure 1.
Fig. 1. D 'H-N-HSQC NMRspectrumofN-labeledTnCshowingthemostcrowdedregion of thespectrum.Residues shown in square bracketsaredegenerate.Residuesmarkedwithanasteriskaretentativeassignments.Boxesareplacedinthe spectrumwherecorrelationswerefundusing 3D techniquesbutwerenotpresetinthisspectrum.

Figure 4.
FEES Lelr 293:72-80. ification of proteinsecondarystructure by HNR spectroscopy.

The above figures are reproduced from the cited reference which is an Open Access publication published by the Protein Society

Secondary reference #2

Title

Calcium-Induced dimerization of troponin c: mode of interaction and use of trifluoroethanol as a denaturant of quaternary structure.

Authors

C.M.Slupsky, C.M.Kay, F.C.Reinach, L.B.Smillie, B.D.Sykes.

Ref.

Biochemistry, 1995, 34, 7365-7375. [DOI no: 10.1021/bi00022a009]

PubMed id

7779778