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==Solution NMR structure of the ternary complex of human ileal bile acid-binding protein with glycocholate and glycochenodeoxycholate==
==Solution NMR structure of the ternary complex of human ileal bile acid-binding protein with glycocholate and glycochenodeoxycholate==
<StructureSection load='2mm3' size='340' side='right' caption='[[2mm3]], [[NMR_Ensembles_of_Models | 10 NMR models]]' scene=''>
<StructureSection load='2mm3' size='340' side='right'caption='[[2mm3]]' scene=''>
== Structural highlights ==
== Structural highlights ==
<table><tr><td colspan='2'>[[2mm3]] is a 1 chain structure. Full experimental information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=2MM3 OCA]. For a <b>guided tour on the structure components</b> use [http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=2MM3 FirstGlance]. <br>
<table><tr><td colspan='2'>[[2mm3]] is a 1 chain structure with sequence from [https://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens]. Full experimental information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=2MM3 OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=2MM3 FirstGlance]. <br>
</td></tr><tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat"><scene name='pdbligand=CHO:GLYCOCHENODEOXYCHOLIC+ACID'>CHO</scene>, <scene name='pdbligand=GCH:GLYCOCHOLIC+ACID'>GCH</scene></td></tr>
</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">Solution NMR</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=2mm3 FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=2mm3 OCA], [http://www.rcsb.org/pdb/explore.do?structureId=2mm3 RCSB], [http://www.ebi.ac.uk/pdbsum/2mm3 PDBsum]</span></td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=CHO:GLYCOCHENODEOXYCHOLIC+ACID'>CHO</scene>, <scene name='pdbligand=GCH:GLYCOCHOLIC+ACID'>GCH</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=2mm3 FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=2mm3 OCA], [https://pdbe.org/2mm3 PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=2mm3 RCSB], [https://www.ebi.ac.uk/pdbsum/2mm3 PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=2mm3 ProSAT]</span></td></tr>
</table>
</table>
== Function ==
== Function ==
[[http://www.uniprot.org/uniprot/FABP6_HUMAN FABP6_HUMAN]] Ileal protein which stimulates gastric acid and pepsinogen secretion. Seems to be able to bind to bile salts and bilirubins. Isoform 2 is essential for the survival of colon cancer cells to bile acid-induced apoptosis.<ref>PMID:17909007</ref>
[https://www.uniprot.org/uniprot/FABP6_HUMAN FABP6_HUMAN] Ileal protein which stimulates gastric acid and pepsinogen secretion. Seems to be able to bind to bile salts and bilirubins. Isoform 2 is essential for the survival of colon cancer cells to bile acid-induced apoptosis.<ref>PMID:17909007</ref>  
<div style="background-color:#fffaf0;">
<div style="background-color:#fffaf0;">
== Publication Abstract from PubMed ==
== Publication Abstract from PubMed ==
Human ileal bile acid binding protein (I-BABP) is a member of the family of intracellular lipid-binding proteins and is thought to play a role in the enterohepatic circulation of bile salts. Our group has previously shown that human I-BABP binds two molecules of glycocholate (GCA) with low intrinsic affinity but an extraordinary high degree of positive cooperativity. Besides the strong positive cooperativity, human I-BABP exhibits a high degree of site selectivity in its interactions with GCA and glycochenodeoxycholate (GCDA), the two major bile salts in humans. In this study, on the basis of our first generation nuclear magnetic resonance (NMR) structure of the ternary complex of human I-BABP with GCA and GCDA, we introduced single-residue mutations at certain key positions in the binding pocket that might disrupt a hydrogen-bonding network, a likely way of energetic communication between the two sites. Macroscopic binding parameters were determined using isothermal titration calorimetry, and site selectivity was monitored by NMR spectroscopy of isotopically enriched bile salts. According to our results, cooperativity and site selectivity are not linked in human I-BABP. While cooperativity is governed by a subtle interplay of entropic and enthalpic contributions, site selectivity appears to be determined by more localized enthalpic effects. Possible communication pathways between the two binding sites are discussed.
Besides aiding digestion, bile salts are important signal molecules exhibiting a regulatory role in metabolic processes. Human ileal bile acid-binding protein (hI-BABP) is an intracellular carrier of bile salts in the epithelial cells of the distal small intestine and has a key role in the enterohepatic circulation of bile salts. Positive binding cooperativity combined with site-selectivity of glycocholate (GCA) and glycochenodeoxycholate (GCDA), the two most abundant bile salts in the human body, makes hI-BABP a unique member of the family of intracellular lipid binding proteins (iLBP). Solution NMR structure of the ternary complex of human I-BABP with GCA and GCDA reveals an extensive network of hydrogen bonds and hydrophobic interactions stabilizing the bound bile salts. Conformational changes accompanying bile salt binding affects four major regions in the protein including the C/D, E/F, and G/H loops as well as the helical segment. Most of these protein regions coincide with a previously described network of millisecond time scale fluctuations in the apo protein, a motion absent in the bound state. Comparison of the heterotypic doubly-ligated complex with the unligated form provides further evidence of a conformation selection mechanism of ligand entry. Structural and dynamic aspects of human I-BABP-bile salt interaction is discussed and compared with characteristics of ligand binding in other members of the iLBP family. This article is protected by copyright. All rights reserved.


Determinants of cooperativity and site selectivity in human ileal bile acid binding protein.,Toke O, Monsey JD, DeKoster GT, Tochtrop GP, Tang C, Cistola DP Biochemistry. 2006 Jan 24;45(3):727-37. PMID:16411748<ref>PMID:16411748</ref>
Structural determinants of ligand binding in the ternary complex of human ileal bile acid-binding protein with glycocholate and glycochenodeoxycholate obtained from solution NMR.,Horvath G, Bencsura A, Simon A, Tochtrop GP, DeKoster GT, Covey DF, Cistola DP, Toke O FEBS J. 2015 Nov 27. doi: 10.1111/febs.13610. PMID:26613247<ref>PMID:26613247</ref>


From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
</div>
</div>
<div class="pdbe-citations 2mm3" style="background-color:#fffaf0;"></div>
==See Also==
*[[Fatty acid-binding protein 3D structures|Fatty acid-binding protein 3D structures]]
== References ==
== References ==
<references/>
<references/>
__TOC__
__TOC__
</StructureSection>
</StructureSection>
[[Category: Bencsura, A]]
[[Category: Homo sapiens]]
[[Category: Cistola, D P]]
[[Category: Large Structures]]
[[Category: Covey, D F]]
[[Category: Bencsura A]]
[[Category: DeKoster, G T]]
[[Category: Cistola DP]]
[[Category: Egyed, O]]
[[Category: Covey DF]]
[[Category: Horvath, G]]
[[Category: DeKoster GT]]
[[Category: Simon, A]]
[[Category: Egyed O]]
[[Category: Tochtrop, G P]]
[[Category: Horvath G]]
[[Category: Toke, O]]
[[Category: Simon A]]
[[Category: Enterohepatic circulation]]
[[Category: Tochtrop GP]]
[[Category: Lipid binding protein]]
[[Category: Toke O]]
[[Category: Lipid-binding protein]]
[[Category: Orthogonal beta sheet]]
[[Category: Positive binding cooperativity]]
[[Category: Site-selectivity]]

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