2sas
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STRUCTURE OF A SARCOPLASMIC CALCIUM-BINDING PROTEIN FROM AMPHIOXUS REFINED AT 2.4 ANGSTROMS RESOLUTION
OverviewOverview
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.
About this StructureAbout this Structure
2SAS is a Single protein structure of sequence from Branchiostoma lanceolatum with CA as ligand. Full crystallographic information is available from OCA.
ReferenceReference
Structure of a sarcoplasmic calcium-binding protein from amphioxus refined at 2.4 A resolution., Cook WJ, Jeffrey LC, Cox JA, Vijay-Kumar S, J Mol Biol. 1993 Jan 20;229(2):461-71. PMID:8429557
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