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PDBsum entry 1qq0
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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A closer look at the active site of gamma-Class carbonic anhydrases: high-Resolution crystallographic studies of the carbonic anhydrase from methanosarcina thermophila.
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Authors
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T.M.Iverson,
B.E.Alber,
C.Kisker,
J.G.Ferry,
D.C.Rees.
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Ref.
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Biochemistry, 2000,
39,
9222-9231.
[DOI no: ]
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PubMed id
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Abstract
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The prototype of the gamma-class of carbonic anhydrase has been characterized
from the methanogenic archaeon Methanosarcina thermophila. Previously reported
kinetic studies of the gamma-class carbonic anhydrase are consistent with this
enzyme having a reaction mechanism similar to that of the mammalian alpha-class
carbonic anhydrase. However, the overall folds of these two enzymes are
dissimilar, and apart from the zinc-coordinating histidines, the active site
residues bear little resemblance to one another. The crystal structures of
zinc-containing and cobalt-substituted gamma-class carbonic anhydrases from M.
thermophila are reported here between 1.46 and 1.95 A resolution in the unbound
form and cocrystallized with either SO(4)(2)(-) or HCO(3)(-). Relative to the
tetrahedral coordination geometry seen at the active site in the alpha-class of
carbonic anhydrases, the active site of the gamma-class enzyme contains
additional metal-bound water ligands, so the overall coordination geometry is
trigonal bipyramidal for the zinc-containing enzyme and octahedral for the
cobalt-substituted enzyme. Ligands bound to the active site all make contacts
with the side chain of Glu 62 in manners that suggest the side chain is likely
protonated. In the uncomplexed zinc-containing enzyme, the side chains of Glu 62
and Glu 84 appear to share a proton; additionally, Glu 84 exhibits multiple
conformations. This suggests that Glu 84 may act as a proton shuttle, which is
an important aspect of the reaction mechanism of alpha-class carbonic
anhydrases. A hydrophobic pocket on the surface of the enzyme may participate in
the trapping of CO(2) at the active site. On the basis of the coordination
geometry at the active site, ligand binding modes, the behavior of the side
chains of Glu 62 and Glu 84, and analogies to the well-characterized alpha-class
of carbonic anhydrases, a more-defined reaction mechanism is proposed for the
gamma-class of carbonic anhydrases.
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Secondary reference #1
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Title
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A left-Hand beta-Helix revealed by the crystal structure of a carbonic anhydrase from the archaeon methanosarcina thermophila.
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Authors
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C.Kisker,
H.Schindelin,
B.E.Alber,
J.G.Ferry,
D.C.Rees.
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Ref.
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Embo J, 1996,
15,
2323-2330.
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PubMed id
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