View source for 3rsd


==STRUCTURE OF THE D121N VARIANT OF RIBONUCLEASE A==
<StructureSection load='3rsd' size='340' side='right' caption='[[3rsd]], [[Resolution|resolution]] 1.60&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[3rsd]] is a 1 chain structure with sequence from [http://en.wikipedia.org/wiki/Bovin Bovin]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=3RSD OCA]. For a <b>guided tour on the structure components</b> use [http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=3RSD FirstGlance]. <br>
</td></tr><tr id='activity'><td class="sblockLbl"><b>Activity:</b></td><td class="sblockDat"><span class='plainlinks'>[http://en.wikipedia.org/wiki/Pancreatic_ribonuclease Pancreatic ribonuclease], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.1.27.5 3.1.27.5] </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=3rsd FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=3rsd OCA], [http://pdbe.org/3rsd PDBe], [http://www.rcsb.org/pdb/explore.do?structureId=3rsd RCSB], [http://www.ebi.ac.uk/pdbsum/3rsd PDBsum], [http://prosat.h-its.org/prosat/prosatexe?pdbcode=3rsd ProSAT]</span></td></tr>
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== Function ==
[[http://www.uniprot.org/uniprot/RNAS1_BOVIN RNAS1_BOVIN]] Endonuclease that catalyzes the cleavage of RNA on the 3' side of pyrimidine nucleotides. Acts on single stranded and double stranded RNA.<ref>PMID:7479688</ref>  
== 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/rs/3rsd_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=3rsd ConSurf].
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== Publication Abstract from PubMed ==
The side chains of histidine and aspartate residues form a hydrogen bond in the active sites of many enzymes. In serine proteases, the His...Asp hydrogen bond of the catalytic triad is known to contribute greatly to catalysis, perhaps via the formation of a low-barrier hydrogen bond. In bovine pancreatic ribonuclease A (RNase A), the His...Asp dyad is composed of His119 and Asp121. Previously, site-directed mutagenesis was used to show that His119 has a fundamental role, to act as an acid during catalysis of RNA cleavage [Thompson, J. E., and Raines, R. T. (1994) J. Am. Chem. Soc. 116, 5467-5468]. Here, Asp121 was replaced with an asparagine or alanine residue. The crystalline structures of the two variants were determined by X-ray diffraction analysis to a resolution of 1.6 A with an R-factor of 0.18. Replacing Asp121 with an asparagine or alanine residue does not perturb the overall conformation of the enzyme. In the structure of D121N RNase A, Ndelta rather than Odelta of Asn121 faces His119. This alignment in the crystalline state is unlikely to exist in solution because catalysis by the D121N variant is not compromised severely. The steady-state kinetic parameters for catalysis by the wild-type and variant enzymes were determined for the cleavage of uridylyl(3'--&gt;5')adenosine and poly(cytidylic acid), and for the hydrolysis of uridine 2',3'-cyclic phosphate. Replacing Asp121 decreases the values of kcat/Km and kcat for cleavage by 10-fold (D121N) and 10(2)-fold (D121A). Replacing Asp121 also decreases the values of kcat/Km and kcat for hydrolysis by 10(0. 5)-fold (D121N) and 10-fold (D121A) but has no other effect on the pH-rate profiles for hydrolysis. There is no evidence for the formation of a low-barrier hydrogen bond between His119 and either an aspartate or an asparagine residue at position 121. Apparently, the major role of Asp121 is to orient the proper tautomer of His119 for catalysis. Thus, the mere presence of a His...Asp dyad in an enzymic active site is not a mandate for its being crucial in effecting catalysis.

His...Asp catalytic dyad of ribonuclease A: structure and function of the wild-type, D121N, and D121A enzymes.,Schultz LW, Quirk DJ, Raines RT Biochemistry. 1998 Jun 23;37(25):8886-98. PMID:9636030<ref>PMID:9636030</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 3rsd" style="background-color:#fffaf0;"></div>

==See Also==
*[[Ribonuclease|Ribonuclease]]
*[[Temp|Temp]]
== References ==
<references/>
__TOC__
</StructureSection>
[[Category: Bovin]]
[[Category: Pancreatic ribonuclease]]
[[Category: Quirk, D J]]
[[Category: Raines, R T]]
[[Category: Schultz, L W]]
[[Category: Endonuclease]]
[[Category: Hydrolase]]
[[Category: Ribonuclease some]]
[[Category: Site-directed mutagenesis]]