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[[Image:1cal.gif|left|200px]]<br /><applet load="1cal" size="350" color="white" frame="true" align="right" spinBox="true"
caption="1cal, resolution 2.2&Aring;" />
'''STRUCTURAL ANALYSIS OF THE ZINC HYDROXIDE-THR 199-GLU 106 HYDROGEN BONDING NETWORK IN HUMAN CARBONIC ANHYDRASE II'''<br />


==Overview==
==STRUCTURAL ANALYSIS OF THE ZINC HYDROXIDE-THR 199-GLU 106 HYDROGEN BONDING NETWORK IN HUMAN CARBONIC ANHYDRASE II==
The significance of the zinc hydroxide-Thr-199-Glu-106 hydrogen-bond network in the active site of human carbonic anhydrase II has been examined by X-ray crystallographic analyses of site-specific mutants. Mutants with Ala-199 and Ala-106 or Gln-106 have low catalytic activities, while a mutant with Asp-106 has almost full CO2 hydration activity. The structures of these four mutants, as well as that of the bicarbonate complex of the mutant with Ala-199, have been determined at 1.7 to 2.2 A resolution. Removal of the gamma atoms of residue 199 leads to a distorted tetrahedral geometry at the zinc ion, and a catalytically important zinc-bound water molecule has moved towards Glu-106. In the bicarbonate complex of the mutant with Ala-199 one oxygen atom from bicarbonate binds to zinc without displacing this water molecule. Tetrahedral coordination geometries are retained in the mutants at position 106. The mutants with Ala-106 and Gln-106 have a zinc-bound sulfate ion, whereas this sulfate site is only partially occupied in the mutant with Asp-106. The hydrogen-bond network seems to be "reversed" in the mutants with Ala-106 and Gln-106. The network is preserved as in native enzyme in the mutant with Asp-106 but the side chain of Asp-106 is more extended than that of Glu-106 in the native enzyme. These results illustrate the importance of Glu-106 and Thr-199 for controlling the precise coordination geometry of the zinc ion and its ligand preferences which results in an optimal orientation of a zinc-bound hydroxide ion for an attack on the CO2 substrate.
<StructureSection load='1cal' size='340' side='right'caption='[[1cal]], [[Resolution|resolution]] 2.20&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[1cal]] 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=1CAL OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=1CAL 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]] 2.2&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><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=1cal FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=1cal OCA], [https://pdbe.org/1cal PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=1cal RCSB], [https://www.ebi.ac.uk/pdbsum/1cal PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=1cal 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/ca/1cal_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=1cal ConSurf].
<div style="clear:both"></div>


==Disease==
==See Also==
Known disease associated with this structure: Osteopetrosis, autosomal recessive 3, with renal tubular acidosis OMIM:[[http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=611492 611492]]
*[[Carbonic anhydrase 3D structures|Carbonic anhydrase 3D structures]]
 
== References ==
==About this Structure==
<references/>
1CAL is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Homo_sapiens Homo sapiens] with <scene name='pdbligand=ZN:'>ZN</scene> as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/Carbonate_dehydratase Carbonate dehydratase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=4.2.1.1 4.2.1.1] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1CAL OCA].
__TOC__
 
</StructureSection>
==Reference==
Structural analysis of the zinc hydroxide-Thr-199-Glu-106 hydrogen-bond network in human carbonic anhydrase II., Xue Y, Liljas A, Jonsson BH, Lindskog S, Proteins. 1993 Sep;17(1):93-106. PMID:[http://ispc.weizmann.ac.il//pmbin/getpm?pmid=7901850 7901850]
[[Category: Carbonate dehydratase]]
[[Category: Homo sapiens]]
[[Category: Homo sapiens]]
[[Category: Single protein]]
[[Category: Large Structures]]
[[Category: Jonsson, B H.]]
[[Category: Jonsson B-H]]
[[Category: Liljas, A.]]
[[Category: Liljas A]]
[[Category: Lindskog, S.]]
[[Category: Lindskog S]]
[[Category: Xue, Y.]]
[[Category: Xue Y]]
[[Category: ZN]]
[[Category: lyase(oxo-acid)]]
 
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