View source for 2nxs


==Structural and kinetic effects of hydrophobic mutations in the active site of human carbonic anhydrase II==
<StructureSection load='2nxs' size='340' side='right'caption='[[2nxs]], [[Resolution|resolution]] 1.80&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[2nxs]] 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=2NXS OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=2NXS 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]] 1.8&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=SO4:SULFATE+ION'>SO4</scene>, <scene name='pdbligand=ZN:ZINC+ION'>ZN</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=2nxs FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=2nxs OCA], [https://pdbe.org/2nxs PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=2nxs RCSB], [https://www.ebi.ac.uk/pdbsum/2nxs PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=2nxs ProSAT]</span></td></tr>
</table>
== Disease ==
[https://www.uniprot.org/uniprot/CAH2_HUMAN CAH2_HUMAN] Defects in CA2 are the cause of osteopetrosis autosomal recessive type 3 (OPTB3) [MIM:[https://omim.org/entry/259730 259730]; also known as osteopetrosis with renal tubular acidosis, carbonic anhydrase II deficiency syndrome, Guibaud-Vainsel syndrome or marble brain disease. Osteopetrosis is a rare genetic disease characterized by abnormally dense bone, due to defective resorption of immature bone. The disorder occurs in two forms: a severe autosomal recessive form occurring in utero, infancy, or childhood, and a benign autosomal dominant form occurring in adolescence or adulthood. Autosomal recessive osteopetrosis is usually associated with normal or elevated amount of non-functional osteoclasts. OPTB3 is associated with renal tubular acidosis, cerebral calcification (marble brain disease) and in some cases with mental retardation.<ref>PMID:1928091</ref> <ref>PMID:1542674</ref> <ref>PMID:8834238</ref> <ref>PMID:9143915</ref> <ref>PMID:15300855</ref> 
== Function ==
[https://www.uniprot.org/uniprot/CAH2_HUMAN CAH2_HUMAN] Essential for bone resorption and osteoclast differentiation (By similarity). Reversible hydration of carbon dioxide. Can hydrate cyanamide to urea. Involved in the regulation of fluid secretion into the anterior chamber of the eye.<ref>PMID:10550681</ref> <ref>PMID:11831900</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/nx/2nxs_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=2nxs ConSurf].
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== Publication Abstract from PubMed ==
Catalysis of the hydration of CO2 by human carbonic anhydrase isozyme II (HCA II) is sustained at a maximal catalytic turnover of 1 mus-1 by proton transfer between a zinc-bound solvent and bulk solution. This mechanism of proton transfer is facilitated via the side chain of His64, which is located 7.5 A from the zinc, and mediated via intervening water molecules in the active-site cavity. Three hydrophilic residues that have previously been shown to contribute to the stabilization of these intervening waters were replaced with hydrophobic residues (Y7F, N62L, and N67L) to determine their effects on proton transfer. The structures of all three mutants were determined by X-ray crystallography, with crystals equilibrated from pH 6.0 to 10.0. A range of changes were observed in the ordered solvent and the conformation of the side chain of His64. Correlating these structural variants with kinetic studies suggests that the very efficient proton transfer (approximately 7 micros-1) observed for Y7F HCA II in the dehydration direction, compared with the wild type and other mutants of this study, is due to a combination of three features. First, in this mutant, the side chain of His64 showed an appreciable inward orientation pointing toward the active-site zinc. Second, in the structure of Y7F HCA II, there is an unbranched chain of hydrogen-bonded waters linking the proton donor His64 and acceptor zinc-bound hydroxide. Finally, the difference in pKa of the donor and acceptor appears favorable for proton transfer. The data suggest roles for residues 7, 62, and 67 in fine-tuning the properties of His64 for optimal proton transfer in catalysis.

Speeding up proton transfer in a fast enzyme: kinetic and crystallographic studies on the effect of hydrophobic amino acid substitutions in the active site of human carbonic anhydrase II.,Fisher SZ, Tu C, Bhatt D, Govindasamy L, Agbandje-McKenna M, McKenna R, Silverman DN Biochemistry. 2007 Mar 27;46(12):3803-13. Epub 2007 Mar 2. PMID:17330962<ref>PMID:17330962</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 2nxs" style="background-color:#fffaf0;"></div>

==See Also==
*[[Carbonic anhydrase 3D structures|Carbonic anhydrase 3D structures]]
== References ==
<references/>
__TOC__
</StructureSection>
[[Category: Homo sapiens]]
[[Category: Large Structures]]
[[Category: Fisher SZ]]
[[Category: McKenna R]]