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PDBsum entry 1qnv
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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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Mad analyses of yeast 5-Aminolaevulinate dehydratase: their use in structure determination and in defining the metal-Binding sites.
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Authors
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P.T.Erskine,
E.M.Duke,
I.J.Tickle,
N.M.Senior,
M.J.Warren,
J.B.Cooper.
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Ref.
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Acta Crystallogr D Biol Crystallogr, 2000,
56,
421-430.
[DOI no: ]
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PubMed id
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Abstract
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MAD experiments attempting to solve the structure of 5--aminolaevulinic acid
dehydratase using Zn and Pb edges are described. The data obtained proved
insufficient for a complete structure solution but were invaluable in subsequent
identification of metal-binding sites using anomalous difference Fourier
analyses once the structure of the enzyme had been solved. These sites include
the highly inhibitory substitution of an enzymic cofactor Zn(2+) ion by Pb(2+)
ions, which represents a major contribution towards understanding the molecular
basis of lead poisoning. The MAD data collected at the Pb edge were also used
with isomorphous replacement data from the same Pb co-crystal and a Hg
co-crystal to provide the first delineation of the enzyme's quaternary
structure. In this MADIR analysis, the Hg co-crystal data were treated as native
data. Anomalous difference Fouriers were again used, revealing that Hg(2+) had
substituted for the same Zn(2+) cofactor ion as had Pb(2+), a finding of
fundamental importance for the understanding of mercury poisoning. In addition,
Pt(2+) ions were found to bind at the same place in the structure. The refined
structures of the Pb- and the Hg-complexed enzymes are presented at 2.5 and 3.0
A resolution, respectively.
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Figure 4.
Figure 4 S. cerevisiae ALAD Pb edge (PX 9.5 MAD  [1]
data) anomalous difference Patterson at 3.0 Å resolution, u = ½
Harker section. The site marked by a cross was tried in a
superposition function in VECSUM but failed to bring back other
sites. It produced poor phasing statistics in MLPHARE. From the
isomorphous replacement processing of the PX 9.6 data from this
crystal against the isomorphous Hg co-crystal the site
corresponds to one of the Pb sites. The major axial peak at the
right corresponds to peaks in that processing found to have
arisen from cross vectors between the two lead sites. The map is
contoured at 94% r.m.s.
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Figure 6.
Figure 6 A MADIR approach with data from the S. cerevisiae ALAD
lead acetate co-crystal allowed the calculation of an
electron-density map at 3.0 Å resolution in which there was a
clear solvent boundary. The map was extended to show the overall
organization of the octamer. Here, four subunits of the ALAD
octamer can be seen disposed around the crystallographic
fourfold axis.
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The above figures are
reprinted
by permission from the IUCr:
Acta Crystallogr D Biol Crystallogr
(2000,
56,
421-430)
copyright 2000.
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