View source for 5cqm


==GTB mutant with mercury - E303C==
<StructureSection load='5cqm' size='340' side='right'caption='[[5cqm]], [[Resolution|resolution]] 1.65&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[5cqm]] is a 1 chain structure with sequence from [https://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=5CQM OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=5CQM 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]] 1.65&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=HG:MERCURY+(II)+ION'>HG</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=5cqm FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=5cqm OCA], [https://pdbe.org/5cqm PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=5cqm RCSB], [https://www.ebi.ac.uk/pdbsum/5cqm PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=5cqm ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/BGAT_HUMAN BGAT_HUMAN] This protein is the basis of the ABO blood group system. The histo-blood group ABO involves three carbohydrate antigens: A, B, and H. A, B, and AB individuals express a glycosyltransferase activity that converts the H antigen to the A antigen (by addition of UDP-GalNAc) or to the B antigen (by addition of UDP-Gal), whereas O individuals lack such activity.
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== Publication Abstract from PubMed ==
The homologous glycosyltransferases alpha-1,3-N-acetylgalactosaminyltransferase (GTA) and alpha-1,3-galactosyltransferase (GTB) carry out the final synthetic step of the closely related human ABO(H) blood group A and B antigens. The catalytic mechanism of these model retaining enzymes remains under debate, where Glu303 has been suggested to act as a putative nucleophile in a double displacement mechanism, a local dipole stabilizing the intermediate in an orthogonal associative mechanism or a general base to stabilize the reactive oxocarbenium ion-like intermediate in an S N i-like mechanism. Kinetic analysis of GTA and GTB point mutants E303C, E303D, E303Q and E303A shows that despite the enzymes having nearly identical sequences, the corresponding mutants of GTA/GTB have up to a 13-fold difference in their residual activities relative to wild type. High-resolution single crystal X-ray diffraction studies reveal, surprisingly, that the mutated Cys, Asp and Gln functional groups are no more than 0.8 A further from the anomeric carbon of donor substrate compared to wild type. However, complicating the analysis is the observation that Glu303 itself plays a critical role in maintaining the stability of a strained "double-turn" in the active site through several hydrogen bonds, and any mutation other than E303Q leads to significantly higher thermal motion or even disorder in the substrate recognition pockets. Thus, there is a remarkable juxtaposition of the mutants E303C and E303D, which retain significant activity despite disrupted active site architecture, with GTB/E303Q, which maintains active site architecture but exhibits zero activity. These findings indicate that nucleophilicity at position 303 is more catalytically valuable than active site stability and highlight the mechanistic elasticity of these enzymes.

Glycosyltransfer in mutants of putative catalytic residue Glu303 of the human ABO(H) A and B blood group glycosyltransferases GTA and GTB proceeds through a labile active site.,Blackler RJ, Gagnon SM, Polakowski R, Rose NL, Zheng RB, Letts JA, Johal AR, Schuman B, Borisova SN, Palcic MM, Evans SV Glycobiology. 2016 Nov 22. PMID:27979997<ref>PMID:27979997</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 5cqm" style="background-color:#fffaf0;"></div>

==See Also==
*[[Glycosyltransferase 3D structures|Glycosyltransferase 3D structures]]
== References ==
<references/>
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</StructureSection>
[[Category: Homo sapiens]]
[[Category: Large Structures]]
[[Category: Blackler RJ]]
[[Category: Gagnon SML]]