 |
PDBsum entry 1uux
|
|
|
|
|
 |
Contents |
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
* Residue conservation analysis
|
|
|
|
|
References listed in PDB file
|
|
|
Key reference
|
|
|
Title
|
|
Structure of the molybdopterin-Bound cnx1g domain links molybdenum and copper metabolism.
|
|
|
Authors
|
|
J.Kuper,
A.Llamas,
H.J.Hecht,
R.R.Mendel,
G.Schwarz.
|
|
|
Ref.
|
|
Nature, 2004,
430,
803-806.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
The molybdenum cofactor is part of the active site of all molybdenum-dependent
enzymes, except nitrogenase. The molybdenum cofactor consists of molybdopterin,
a phosphorylated pyranopterin, with an ene-dithiolate coordinating molybdenum.
The same pyranopterin-based cofactor is involved in metal coordination of the
homologous tungsten-containing enzymes found in archea. The molybdenum cofactor
is synthesized by a highly conserved biosynthetic pathway. In plants, the
multidomain protein Cnx1 catalyses the insertion of molybdenum into
molybdopterin. The Cnx1 G domain (Cnx1G), whose crystal structure has been
determined in its apo form, binds molybdopterin with high affinity and
participates in the catalysis of molybdenum insertion. Here we present two
high-resolution crystal structures of Cnx1G in complex with molybdopterin and
with adenylated molybdopterin (molybdopterin-AMP), a mechanistically important
intermediate. Molybdopterin-AMP is the reaction product of Cnx1G and is
subsequently processed in a magnesium-dependent reaction by the amino-terminal E
domain of Cnx1 to yield active molybdenum cofactor. The unexpected
identification of copper bound to the molybdopterin dithiolate sulphurs in both
structures, coupled with the observed copper inhibition of Cnx1G activity,
provides a molecular link between molybdenum and copper metabolism.
|
|
|
|
|
|
|
|
Figure 1.
Figure 1: Structure of the Cnx1G -MPT and Ser583Ala -MPT -AMP
complexes. a, b, Ribbon representation of Cnx1G (a) and
Ser583Ala (b).  -Helices
and  -strands
are shown in green and orange, respectively. Bound MPT and MPT
-AMP are shown in ball-and-stick notation and are covered by the
2F[o] -F[c] electron density contoured at 1.0  .
The difference density (F[o] -F[c]) is shown in red (3.5 ).
c, d, Close-up views of the bound MPT (c) and AMP (d) regions in
the Ser583Ala structure. e, f, Molecular surface of Ser583Ala
with bound MPT -AMP showing, respectively, residues important
for MPT binding (red) and catalysis12,14 (blue), and the
electrostatic surface potential with  11
kT as borders for electropositive (blue) and negative (red)
regions calculated with SYBIL and GRASP30. The catalytically
important residues Asp 515 and Asp 548 are highlighted. The
position of Mg2+ found in the homologous MoeA^22 domain is
superimposed.
|
|
Figure 4.
Figure 4: Hypothetical mechanism of the molybdenum insertion
reaction. The mechanism of copper chelation is unknown. Cnx1G
adenylates Cu -MPT, a reaction that is thought to be cation
(M2+) dependent. Cnx1E subsequently cleaves the Cu -MPT -AMP
complex to activate and to transfer the molybdenum atom to MPT.
The function of copper is seen in the protection of the reactive
MPT dithiolate.
|
|
|
|
|
|
The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
Nature
(2004,
430,
803-806)
copyright 2004.
|
|
|
|
|
|
|
