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PDBsum entry 1uo9
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Oxidoreductase
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PDB id
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1uo9
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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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The structural basis of cephalosporin formation in a mononuclear ferrous enzyme.
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Authors
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K.Valegård,
A.C.Terwisscha van scheltinga,
A.Dubus,
G.Ranghino,
L.M.Oster,
J.Hajdu,
I.Andersson.
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Ref.
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Nat Struct Mol Biol, 2004,
11,
95.
[DOI no: ]
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PubMed id
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Abstract
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Deacetoxycephalosporin-C synthase (DAOCS) is a mononuclear ferrous enzyme that
transforms penicillins into cephalosporins by inserting a carbon atom into the
penicillin nucleus. In the first half-reaction, dioxygen and 2-oxoglutarate
produce a reactive iron-oxygen species, succinate and CO2. The oxidizing iron
species subsequently reacts with penicillin to give cephalosporin and water.
Here we describe high-resolution structures for ferrous DAOCS in complex with
penicillins, the cephalosporin product, the cosubstrate and the coproduct.
Steady-state kinetic data, quantum-chemical calculations and the new structures
indicate a reaction sequence in which a 'booby-trapped' oxidizing species is
formed. This species is stabilized by the negative charge of succinate on the
iron. The binding sites of succinate and penicillin overlap, and when penicillin
replaces succinate, it removes the stabilizing charge, eliciting oxidative
attack on itself. Requisite groups of penicillin are within 1 A of the expected
position of a ferryl oxygen in the enzyme-penicillin complex.
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Figure 1.
Figure 1. The active site region of DAOCS in complex with
substrates and products. (a) The DAOCS -Fe(II)
-2-oxoglutarate complex2 at 1.5-Å resolution. (b) The DAOCS
-Fe(II) -succinate complex at 1.5-Å resolution. (c) The DAOCS
-Fe(II) -penicillin G complex at 1.6-Å resolution. (d) The DAOCS
-Fe(II) -2-oxoglutarate -penicillin G complex at 1.7 Å
resolution. (e) The DAOCS -Fe(II) -2-oxoglutarate -ampicillin
complex at 1.5-Å resolution. (f) The DAOCS -Fe(II) -DAOC complex
at 1.7-Å resolution. See text for details. The density next to
the penicillin side chain in d,e corresponds to a minor
alternative conformation of the side chain. Dioxygen is expected
to bind at the position of Wat1 in a. The oxygen of the ferryl
iron would be formed at this site^2. The carbon atoms in
2-oxoglutarate are yellow, in succinate orange, in penicillin G
magenta, in ampicillin cyan and in DAOC gold.
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Figure 5.
Figure 5. A possible mechanism for the ring expansion catalyzed
by DAOCS. The mechanism is based on the mode of penicillin
and cephalosporin binding shown in Figures 1d -f and 2. The
presumed oxidation states of the iron are marked. In the
oxidative half reaction, one of the oxygen atoms of dioxygen is
incorporated into succinate while the other one remains on the
iron. This oxygen can remove two electrons and two protons from
the five-membered thiazolidine ring to form the six-membered
dihydrothiazine ring of the cephalosporin product in the
reductive half reaction. Note ligation of the penicillin sulfur
to the iron (Fe -S distance: 2.1 -2.0 Å in the various
complexes) and that both  -
and  -methyl
groups are in van der Waals contact with the iron (iron -methyl
distances: 2.1 -2.5 Å).
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The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
Nat Struct Mol Biol
(2004,
11,
95-0)
copyright 2004.
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