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==STREPTAVIDIN-CYCLO-AC-[CHPQFC]-NH2, PH 4.2==
<StructureSection load='1vwm' size='340' side='right'caption='[[1vwm]], [[Resolution|resolution]] 1.60&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[1vwm]] is a 2 chain structure with sequence from [http://en.wikipedia.org/wiki/As_4.1583 As 4.1583]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1VWM OCA]. For a <b>guided tour on the structure components</b> use [http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=1VWM FirstGlance]. <br>
</td></tr><tr id='NonStdRes'><td class="sblockLbl"><b>[[Non-Standard_Residue|NonStd Res:]]</b></td><td class="sblockDat"><scene name='pdbligand=ACE:ACETYL+GROUP'>ACE</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'>[http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=1vwm FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=1vwm OCA], [http://pdbe.org/1vwm PDBe], [http://www.rcsb.org/pdb/explore.do?structureId=1vwm RCSB], [http://www.ebi.ac.uk/pdbsum/1vwm PDBsum], [http://prosat.h-its.org/prosat/prosatexe?pdbcode=1vwm ProSAT]</span></td></tr>
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== Function ==
[[http://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). 
== Evolutionary Conservation ==
[[Image:Consurf_key_small.gif|200px|right]]
Check<jmol>
  <jmolCheckbox>
    <scriptWhenChecked>; select protein; define ~consurf_to_do selected; consurf_initial_scene = true; script "/wiki/ConSurf/vw/1vwm_consurf.spt"</scriptWhenChecked>
    <scriptWhenUnchecked>script /wiki/extensions/Proteopedia/spt/initialview01.spt</scriptWhenUnchecked>
    <text>to colour the structure by Evolutionary Conservation</text>
  </jmolCheckbox>
</jmol>, as determined by [http://consurfdb.tau.ac.il/ ConSurfDB]. You may read the [[Conservation%2C_Evolutionary|explanation]] of the method and the full data available from [http://bental.tau.ac.il/new_ConSurfDB/main_output.php?pdb_ID=1vwm ConSurf].
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== Publication Abstract from PubMed ==
The pH dependences of the affinities for streptavidin of linear and cyclic peptide ligands containing the HPQ sequence discovered by phage display were determined by plasmon resonance measurements. At pH values ranging from 3.0 to 9.0, the Kd values for Ac-AEFSHPQNTIEGRK-NH2, cyclo-Ac-AE[CHPQGPPC]IEGRK-NH2, and cyclo-Ac-AE[CHPQFC]IEGRK-NH2, were determined by competition, and those for cyclo-[5-S-valeramide-HPQGPPC]K-NH2 were determined directly by equilibrium affinity measurements. The Kd values of the ligands increase by an average factor of 3.0 +/- 0.8 per decrease in pH unit between pH approximately 4.5 and pH approximately 6.3. Below pH approximately 4.5 there is a smaller increase in Kd values, and above pH approximately 6.3 the Kd values become relatively pH-independent. We determined the crystal structures of complexes of streptavidin with cyclo-[5-S-valeramide-HPQGPPC]K-NH2 at pH 1.5, 2.5, 3.0, and 3.5, with cyclo-Ac-[CHPQFC]-NH2 at pH 2.0, 3.0, 3.6, 4.2, 4.8, and 11.8, with cyclo-Ac-[CHPQGPPC]-NH2 at pH 2.5, 2.9, and 3.7, and with FSHPQNT at pH 4.0 and compared the structures with one another and with those previously determined at other pH values. At pH values from 3.0 to 11.8, the electron density for the peptide His side chain is strong, flat, and well defined. A hydrogen bond between the Ndelta1 atom of the His and the peptide Gln amide group indicates the His of the bound peptide in the crystals is uncharged at pH &gt;/= 3.0. By determining selected structures in two different space groups, I222 with two crystallographically inequivalent ligand sites and I4122 with one site, we show that below pH approximately 3.0, the pKa of the bound peptide His in the crystals is influenced by crystal packing interactions. The presence of the Ndelta1His-NGln hydrogen bond along with pH dependences of the peptide affinities suggest that deprotonation of the peptide His is required for high affinity binding of HPQ-containing peptides to streptavidin both in the crystals and in solution.

In crystals of complexes of streptavidin with peptide ligands containing the HPQ sequence the pKa of the peptide histidine is less than 3.0.,Katz BA, Cass RT J Biol Chem. 1997 May 16;272(20):13220-8. PMID:9148939<ref>PMID:9148939</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 1vwm" style="background-color:#fffaf0;"></div>

==See Also==
*[[Avidin 3D structures|Avidin 3D structures]]
== References ==
<references/>
__TOC__
</StructureSection>
[[Category: As 4 1583]]
[[Category: Large Structures]]
[[Category: Cass, R T]]
[[Category: Katz, B A]]
[[Category: Cyclic peptide discovered by phage display]]