View source for 1i14


==ANALYSIS OF AN INVARIANT ASPARTIC ACID IN HPRTS-GLUTAMIC ACID MUTANT==
<StructureSection load='1i14' size='340' side='right'caption='[[1i14]], [[Resolution|resolution]] 1.92&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[1i14]] is a 2 chain structure with sequence from [https://en.wikipedia.org/wiki/Trypanosoma_cruzi Trypanosoma cruzi]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1I14 OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=1I14 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]] 1.92&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=7HP:7-HYDROXY-PYRAZOLO[4,3-D]PYRIMIDINE'>7HP</scene>, <scene name='pdbligand=MG:MAGNESIUM+ION'>MG</scene>, <scene name='pdbligand=PRP:ALPHA-PHOSPHORIBOSYLPYROPHOSPHORIC+ACID'>PRP</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=1i14 FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=1i14 OCA], [https://pdbe.org/1i14 PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=1i14 RCSB], [https://www.ebi.ac.uk/pdbsum/1i14 PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=1i14 ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/Q4DRC4_TRYCC Q4DRC4_TRYCC] 
== 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/i1/1i14_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=1i14 ConSurf].
<div style="clear:both"></div>
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== Publication Abstract from PubMed ==
The role of an invariant aspartic acid (Asp137) in hypoxanthine phosphoribosyltransferases (HPRTs) was examined by site-directed and saturation mutagenesis, functional analysis, and X-ray crystallography using the HPRT from Trypanosoma cruzi. Alanine substitution (D137A) resulted in a 30-fold decrease of k(cat), suggesting that Asp137 participates in catalysis. Saturation mutagenesis was used to generate a library of mutant HPRTs with random substitutions at position 137, and active enzymes were identified by complementation of a bacterial purine auxotroph. Functional analyses of the mutants, including determination of steady-state kinetic parameters and pH-rate dependence, indicate that glutamic acid or glutamine can replace the wild-type aspartate. However, the catalytic efficiency and pH-rate profile for the structural isosteric mutant, D137N, were similar to the D137A mutant. Crystal structures of four of the mutant enzymes were determined in ternary complex with substrate ligands. Structures of the D137E and D137Q mutants reveal potential hydrogen bonds, utilizing several bound water molecules in addition to protein atoms, that position these side chains within hydrogen bond distance of the bound purine analogue, similar in position to the aspartate in the wild-type structure. The crystal structure of the D137N mutant demonstrates that the Asn137 side chain does not form interactions with the purine substrate but instead forms novel interactions that cause the side chain to adopt a nonfunctional rotamer. The results from these structural and functional analyses demonstrate that HPRTs do not require a general base at position 137 for catalysis. Instead, hydrogen bonding sufficiently stabilizes the developing partial positive charge at the N7-atom of the purine substrate in the transition-state to promote catalysis.

The role for an invariant aspartic acid in hypoxanthine phosphoribosyltransferases is examined using saturation mutagenesis, functional analysis, and X-ray crystallography.,Canyuk B, Focia PJ, Eakin AE Biochemistry. 2001 Mar 6;40(9):2754-65. PMID:11258886<ref>PMID:11258886</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 1i14" style="background-color:#fffaf0;"></div>

==See Also==
*[[Phosphoribosyltransferase 3D structures|Phosphoribosyltransferase 3D structures]]
== References ==
<references/>
__TOC__
</StructureSection>
[[Category: Large Structures]]
[[Category: Trypanosoma cruzi]]
[[Category: Canyuk B]]
[[Category: Eakin AE]]
[[Category: Focia PJ]]