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PDBsum entry 1pl4
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Oxidoreductase
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PDB id
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1pl4
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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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Amino acid substitution at the dimeric interface of human manganese superoxide dismutase.
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Authors
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A.S.Hearn,
L.Fan,
J.R.Lepock,
J.P.Luba,
W.B.Greenleaf,
D.E.Cabelli,
J.A.Tainer,
H.S.Nick,
D.N.Silverman.
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Ref.
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J Biol Chem, 2004,
279,
5861-5866.
[DOI no: ]
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PubMed id
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Abstract
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The side chains of His30 and Tyr166 from adjacent subunits in the homotetramer
human manganese superoxide dismutase (Mn-SOD) form a hydrogen bond across the
dimer interface and participate in a hydrogen-bonded network that extends to the
active site. Compared with wild-type Mn-SOD, the site-specific mutants H30N,
Y166F, and the corresponding double mutant showed 10-fold decreases in
steady-state constants for catalysis measured by pulse radiolysis. The
observation of no additional effect upon the second mutation is an example of
cooperatively interacting residues. A similar effect was observed in the thermal
stability of these enzymes; the double mutant did not reduce the major unfolding
transition to an extent greater than either single mutant. The crystal
structures of these site-specific mutants each have unique conformational
changes, but each has lost the hydrogen bond across the dimer interface, which
results in a decrease in catalysis. These same mutations caused an enhancement
of the dissociation of the product-inhibited complex. That is, His30 and Tyr166
in wild-type Mn-SOD act to prolong the lifetime of the inhibited complex. This
would have a selective advantage in blocking a cellular overproduction of toxic
H2O2.
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Figure 2.
FIG. 2. The least squares superimposed structures of
wild-type human Mn-SOD (purple) and Y166F Mn-SOD (green) showing
residues in the active site. In the mutant, the side chain of
Asn171(B) emanating from the adjacent residue has rotated
130° around the C-  -C-  bond to form a hydrogen
bond with His30. The side chain of His30 has also rotated
98° around the C- -C- bond overlapping the
site of a water molecule in the wild type.
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Figure 3.
FIG. 3. The least squares superimposed structures of
wild-type human Mn-SOD (purple) and H30N/Y166F Mn-SOD (yellow)
showing residues in the active site. Similar to Asn171(B) in the
single mutant, this side chain turned toward subunit A in the
double mutant, but there is no hydrogen bond between Asn171(B)
and Asn30(A). Instead, the N  -2 of Asn30 formed a
weak hydrogen bond with the phenolic OH of Tyr34.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2004,
279,
5861-5866)
copyright 2004.
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