View source for 1swg


==CIRCULAR PERMUTED STREPTAVIDIN E51/A46 IN COMPLEX WITH BIOTIN==
<StructureSection load='1swg' size='340' side='right'caption='[[1swg]], [[Resolution|resolution]] 1.80&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[1swg]] is a 4 chain structure with sequence from [https://en.wikipedia.org/wiki/Streptomyces_avidinii Streptomyces avidinii]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1SWG OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=1SWG FirstGlance]. <br>
</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">X-ray diffraction, [[Resolution|Resolution]] 1.8&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=BTN:BIOTIN'>BTN</scene></td></tr>
<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=1swg FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=1swg OCA], [https://pdbe.org/1swg PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=1swg RCSB], [https://www.ebi.ac.uk/pdbsum/1swg PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=1swg ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/SAV_STRAV SAV_STRAV] The biological function of streptavidin is not known. Forms a strong non-covalent specific complex with biotin (one molecule of biotin per subunit of streptavidin).
<div style="background-color:#fffaf0;">
== Publication Abstract from PubMed ==
A circularly permuted streptavidin (CP51/46) has been designed to remove the flexible polypeptide loop that undergoes an open to closed conformational change when biotin is bound. The original termini have been joined by a tetrapeptide linker, and four loop residues have been removed, resulting in the creation of new N- and C-termini. Isothermal titration calorimetric studies show that the association constant has been reduced approximately six orders of magnitude below that of wild-type streptavidin to 10(7) M(-1). The deltaH degrees of biotin association for CP51/46 is reduced by 11.1 kcal/mol. Crystal structures of CP51/46 and its biotin complex show no significant alterations in the binding site upon removal of the loop. A hydrogen bond between Ser45 and Ser52 found in the absence of biotin is broken in the closed conformation as the side-chain hydroxyl of Ser45 moves to hydrogen bond to a ureido nitrogen of biotin. This is true in both the wild-type and CP51/46 forms of the protein, and the hydrogen bonding interaction might thus help nucleate closure of the loop. The reduced entropic cost of binding biotin to CP51/46 is consistent with the removal of this loop and a reduction in entropic costs associated with loop closure and immobilization. The reduced enthalpic contribution to the free energy of binding is not readily explainable in terms of the molecular structure, as the binding contacts are nearly entirely conserved, and only small differences in solvent accessible surfaces are observed relative to wild-type streptavidin.

Thermodynamic and structural consequences of flexible loop deletion by circular permutation in the streptavidin-biotin system.,Chu V, Freitag S, Le Trong I, Stenkamp RE, Stayton PS Protein Sci. 1998 Apr;7(4):848-59. PMID:9568892<ref>PMID:9568892</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
</div>
<div class="pdbe-citations 1swg" style="background-color:#fffaf0;"></div>

==See Also==
*[[Avidin 3D structures|Avidin 3D structures]]
== References ==
<references/>
__TOC__
</StructureSection>
[[Category: Large Structures]]
[[Category: Streptomyces avidinii]]
[[Category: Chu V]]
[[Category: Freitag S]]
[[Category: Le Trong I]]
[[Category: Stayton PS]]
[[Category: Stenkamp RE]]