PDBsum entry 2sas

Calcium-binding protein

PDB id: 2sas

Contents

Protein chain

185 a.a.

Metals

_CA ×3

Waters ×1

References listed in PDB file

Key reference

• Title: Structure of a sarcoplasmic calcium-Binding protein from amphioxus refined at 2.4 a resolution.
• Authors: W.J.Cook, L.C.Jeffrey, J.A.Cox, S.Vijay-Kumar.
• Ref.: J Mol Biol, 1993, 229, 461-471.
• PubMed id: 8429557

Abstract

The three-dimensional structure of a sarcoplasmic Ca(2+)-binding protein from the protochordate amphioxus has been determined at 2.4 A resolution using multiple-isomorphous-replacement techniques. The refined model includes all 185 residues, three calcium ions, and one water molecule. The final crystallographic R-factor is 0.199. Bond lengths and bond angles in the molecules have root-mean-square deviations from ideal values of 0.015 A and 2.8 degrees, respectively. The overall structure is highly compact and globular with a predominantly hydrophobic core, unlike the extended dumbbell-shaped structures of calmodulin or troponin C. There are four distinct domains with the typical helix-loop-helix Ca(2+)-binding motif (EF hand). The conformation of the pair of EF hands in the N-terminal half of the protein is unusual due to the presence of an aspartate residue in the twelfth position of the first Ca(2+)-binding loop, rather than the usual glutamate. The C-terminal half of the molecule contains one Ca(2+)-binding domain with a novel helix-loop-helix conformation and one Ca(2+)-binding domain that is no longer functional because of amino acid changes. The overall structure is quite similar to a sarcoplasmic Ca(2+)-binding protein from sandworm, although there is only about 12% amino acid sequence identity between them. The similarity of the structures of these two proteins suggests that all sarcoplasmic Ca(2+)-binding proteins will have the same general conformation, even though there is very little conservation of primary structure among the proteins from various species.

Secondary reference #1

• Title: Crystallization and preliminary X-Ray investigation of a sarcoplasmic calcium-Binding protein from amphioxus.
• Authors: W.J.Cook, Y.S.Babu, J.A.Cox.
• Ref.: J Mol Biol, 1991, 221, 1071-1073.
• PubMed id: 1942041