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==Engineered streptavidin variant (VTAR) in complex with the Twin-Strep-tag peptide==
<StructureSection load='6sok' size='340' side='right'caption='[[6sok]], [[Resolution|resolution]] 1.96&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[6sok]] is a 8 chain structure with sequence from [https://en.wikipedia.org/wiki/Streptomyces_avidinii Streptomyces avidinii] and [https://en.wikipedia.org/wiki/Synthetic_construct Synthetic construct]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=6SOK OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=6SOK 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]] 1.96&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=BE2:2-AMINOBENZOIC+ACID'>BE2</scene>, <scene name='pdbligand=NH2:AMINO+GROUP'>NH2</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=6sok FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=6sok OCA], [https://pdbe.org/6sok PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=6sok RCSB], [https://www.ebi.ac.uk/pdbsum/6sok PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=6sok 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).
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== Publication Abstract from PubMed ==
The affinity system based on the artificial peptide ligand Strep-tag(R) II and engineered tetrameric streptavidin, known as Strep-Tactin(R), offers attractive applications for the study of recombinant proteins, from detection and purification to functional immobilization. To further improve binding of the Strep-tag II to streptavidin we have subjected two protruding loops that shape its ligand pocket for the peptide - instead of D-biotin recognized by the natural protein - to iterative random mutagenesis. Sequence analyses of hits from functional screening assays revealed several unexpected structural motifs, such as a disulfide bridge at the base of one loop, replacement of the crucial residue Trp120 by Gly and a two-residue deletion in the second loop. The mutant m1-9 (dubbed Strep-Tactin XT) showed strongly enhanced affinity towards the Strep-tag II, which was further boosted in case of the bivalent Twin-Strep-tag(R). Four representative streptavidin mutants were crystallized in complex with the Strep-tag II peptide and their X-ray structures were solved at high resolutions. In addition, the crystal structure of the complex between Strep-Tactin XT and the Twin-Strep-tag was elucidated, indicating a bivalent mode of binding and explaining the experimentally observed avidity effect. Our study illustrates the structural plasticity of streptavidin as a scaffold for ligand binding and reveals interaction modes that would have been difficult to predict. As result, Strep-Tactin XT offers a convenient reagent for the kinetically stable immobilization of recombinant proteins fused with the Twin-Strep-tag. The possibility of reversibly dissociating such complexes simply with D-biotin as a competing ligand enables functional studies in protein science as well as cell biology.

The Role of Changing Loop Conformations in Streptavidin Versions Engineered for High-affinity Binding of the Strep-tag II Peptide.,Schmidt TGM, Eichinger A, Schneider M, Bonet L, Carl U, Karthaus D, Theobald I, Skerra A J Mol Biol. 2021 Apr 30;433(9):166893. doi: 10.1016/j.jmb.2021.166893. Epub 2021 , Feb 24. PMID:33639211<ref>PMID:33639211</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
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<div class="pdbe-citations 6sok" style="background-color:#fffaf0;"></div>

==See Also==
*[[Avidin 3D structures|Avidin 3D structures]]
== References ==
<references/>
__TOC__
</StructureSection>
[[Category: Large Structures]]
[[Category: Streptomyces avidinii]]
[[Category: Synthetic construct]]
[[Category: Eichinger A]]
[[Category: Skerra A]]