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PDBsum entry 1qws
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Oxidoreductase
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PDB id
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1qws
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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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An electrical potential in the access channel of catalases enhances catalysis.
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Authors
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P.Chelikani,
X.Carpena,
I.Fita,
P.C.Loewen.
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Ref.
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J Biol Chem, 2003,
278,
31290-31296.
[DOI no: ]
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PubMed id
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Abstract
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Substrate H2O2 must gain access to the deeply buried active site of catalases
through channels of 30-50 A in length. The most prominent or main channel
approaches the active site perpendicular to the plane of the heme and contains a
number of residues that are conserved in all catalases. Changes in Val169, 8 A
from the heme in catalase HPII from Escherichia coli, introducing smaller,
larger or polar side chains reduces the catalase activity. Changes in Asp181, 12
A from the heme, reduces activity by up to 90% if the negatively charged side
chain is removed when Ala, Gln, Ser, Asn, or Ile are the substituted residues.
Only the D181E variant retains wild type activity. Determination of the crystal
structures of the Glu181, Ala181, Ser181, and Gln181 variants of HPII reveals
lower water occupancy in the main channel of the less active variants,
particularly at the position forming the sixth ligand to the heme iron and in
the hydrophobic, constricted region adjacent to Val169. It is proposed that an
electrical potential exists between the negatively charged aspartate (or
glutamate) side chain at position 181 and the positively charged heme iron 12 A
distant. The potential field acts upon the electrical dipoles of water
generating a common orientation that favors hydrogen bond formation and promotes
interaction with the heme iron. Substrate hydrogen peroxide would be affected
similarly and would enter the active site oriented optimally for interaction
with active site residues.
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Figure 3.
FIG. 3. a, schematic showing the distances among waters in
the main channel of the D181E variant. The potential hydrogen
bonds are shown as dashed lines, and the distances are expressed
in Å. The water numbering is as in Fig. 2 and Table IV. b,
stereo view oriented down the main channel toward the heme from
Asp181. The slightly shifted location of the Glu side chain in
the D181E variant is indicated in green. The water numbering is
as in a.
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Figure 4.
FIG. 4. Schematic of the main channel illustrating the
presence of a negative charge (in green) on the side chain of
Glu181 and a positive charge (in green) on the heme iron and the
effect of the electrical potential between these two charges on
the electrical dipoles of water in the channel and active site.
The orientation of the electrical dipoles is indicated by the
green arrow over each H[2]O. The location of the water molecules
are those in subunit A of variant D181E.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2003,
278,
31290-31296)
copyright 2003.
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