2sas: Difference between revisions

[[Image:2sas.jpg|left|200px]]<br /><applet load="2sas" size="350" color="white" frame="true" align="right" spinBox="true"  

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.

2SAS is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Branchiostoma_lanceolatum Branchiostoma lanceolatum] with <scene name='pdbligand=CA:'>CA</scene> as [http://en.wikipedia.org/wiki/ligand ligand]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=2SAS OCA].  

[[Category: Babu, Y S.]]

[[Category: Cook, W J.]]

[[Category: Cox, J A.]]

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