View source for 1uq5

==RICIN A-CHAIN (RECOMBINANT) N122A MUTANT==
<StructureSection load='1uq5' size='340' side='right' caption='[[1uq5]], [[Resolution|resolution]] 1.40&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[1uq5]] is a 1 chain structure with sequence from [http://en.wikipedia.org/wiki/Ricinus_communis Ricinus communis]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1UQ5 OCA]. For a <b>guided tour on the structure components</b> use [http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=1UQ5 FirstGlance]. <br>
</td></tr><tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat"><scene name='pdbligand=ACT:ACETATE+ION'>ACT</scene>, <scene name='pdbligand=SO4:SULFATE+ION'>SO4</scene></td></tr>
<tr id='related'><td class="sblockLbl"><b>[[Related_structure|Related:]]</b></td><td class="sblockDat">[[1apg|1apg]], [[1br5|1br5]], [[1br6|1br6]], [[1fmp|1fmp]], [[1ifs|1ifs]], [[1ift|1ift]], [[1ifu|1ifu]], [[1il3|1il3]], [[1il4|1il4]], [[1il5|1il5]], [[1il9|1il9]], [[1obs|1obs]], [[1obt|1obt]], [[1rtc|1rtc]], [[1uq4|1uq4]], [[2aai|2aai]]</td></tr>
<tr id='activity'><td class="sblockLbl"><b>Activity:</b></td><td class="sblockDat"><span class='plainlinks'>[http://en.wikipedia.org/wiki/rRNA_N-glycosylase rRNA N-glycosylase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.2.2.22 3.2.2.22] </span></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=1uq5 FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=1uq5 OCA], [http://www.rcsb.org/pdb/explore.do?structureId=1uq5 RCSB], [http://www.ebi.ac.uk/pdbsum/1uq5 PDBsum]</span></td></tr>
</table>
== Function ==
[[http://www.uniprot.org/uniprot/RICI_RICCO RICI_RICCO]] Ricin is highly toxic to animal cells and to a lesser extent to plant cells. The A chain acts as a glycosidase that removes a specific adenine residue from an exposed loop of the 28S rRNA (A4324 in mammals), leading to rRNA breakage. As this loop is involved in elongation factor binding, modified ribosomes are catalytically inactive and unable to support protein synthesis. The A chain can inactivate a few thousand ribosomes per minute, faster than the cell can make new ones. Therefore a single A chain molecule can kill an animal cell. The B chain binds to beta-D-galactopyranoside moieties on cell surface glycoproteins and glycolipids and facilitates the entry into the cell of the A chain; B chains are also responsible for cell agglutination (Lectin activity). 
== 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/uq/1uq5_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/chain_selection.php?pdb_ID=2ata ConSurf].
<div style="clear:both"></div>
<div style="background-color:#fffaf0;">
== Publication Abstract from PubMed ==
Models for the binding of the sarcin-ricin loop (SRL) of 28S ribosomal RNA to ricin A chain (RTA) suggest that several surface exposed arginine residues surrounding the active site cleft make important interactions with the RNA substrate. The data presented in this study suggest differing roles for these arginyl residues. Substitution of Arg48 or Arg213 with Ala lowered the activity of RTA 10-fold. Furthermore, substitution of Arg213 with Asp lowered the activity of RTA 100-fold. The crystal structure of this RTA variant showed it to have an unaltered tertiary structure, suggesting that the positively charged state of Arg213 is crucial for activity. Substitution of Arg258 with Ala had no effect on activity, although substitution with Asp lowered activity 10-fold. Substitution of Arg134 prevented expression of folded protein, suggesting a structural role for this residue. Several models have been proposed for the binding of the SRL to the active site of RTA in which the principal difference lies in the conformation of the second 'G' in the target GAGA motif in the 28S rRNA substrate. In one model, the sidechain of Asn122 is proposed to make interactions with this G, whereas another model proposes interactions with Asp75 and Asn78. Site-directed mutagenesis of these residues of RTA favours the first of these models, as substitution of Asn78 with Ser yielded an RTA variant whose activity was essentially wild-type, whereas substitution of Asn122 reduced activity 37.5-fold. Substitution of Asp75 failed to yield significant folded protein, suggesting a structural role for this residue.

The effect of mutations surrounding and within the active site on the catalytic activity of ricin A chain.,Marsden CJ, Fulop V, Day PJ, Lord JM Eur J Biochem. 2004 Jan;271(1):153-62. PMID:14686928<ref>PMID:14686928</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
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==See Also==
*[[Ricin|Ricin]]
== References ==
<references/>
__TOC__
</StructureSection>
[[Category: Ricinus communis]]
[[Category: RRNA N-glycosylase]]
[[Category: Fulop, V]]
[[Category: Marsden, C J]]
[[Category: Glycoprotein]]
[[Category: Glycosidase]]
[[Category: Hydrolase]]
[[Category: Toxin]]