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PDBsum entry 1ce8
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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 binding of inosine monophosphate to escherichia coli carbamoyl phosphate synthetase.
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Authors
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J.B.Thoden,
F.M.Raushel,
G.Wesenberg,
H.M.Holden.
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Ref.
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J Biol Chem, 1999,
274,
22502-22507.
[DOI no: ]
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PubMed id
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Abstract
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Carbamoyl phosphate synthetase (CPS) from Escherichia coli catalyzes the
formation of carbamoyl phosphate, which is subsequently employed in both the
pyrimidine and arginine biosynthetic pathways. The reaction mechanism is known
to proceed through at least three highly reactive intermediates: ammonia,
carboxyphosphate, and carbamate. In keeping with the fact that the product of
CPS is utilized in two competing metabolic pathways, the enzyme is highly
regulated by a variety of effector molecules including potassium and ornithine,
which function as activators, and UMP, which acts as an inhibitor. IMP is also
known to bind to CPS but the actual effect of this ligand on the activity of the
enzyme is dependent upon both temperature and assay conditions. Here we describe
the three-dimensional architecture of CPS with bound IMP determined and refined
to 2.1 A resolution. The nucleotide is situated at the C-terminal portion of a
five-stranded parallel beta-sheet in the allosteric domain formed by Ser(937) to
Lys(1073). Those amino acid side chains responsible for anchoring the nucleotide
to the polypeptide chain include Lys(954), Thr(974), Thr(977), Lys(993),
Asn(1015), and Thr(1017). A series of hydrogen bonds connect the IMP-binding
pocket to the active site of the large subunit known to function in the
phosphorylation of the unstable intermediate, carbamate. This structural
analysis reveals, for the first time, the detailed manner in which CPS
accommodates nucleotide monophosphate effector molecules within the allosteric
domain.
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Figure 3.
Fig. 3. The IMP binding pocket. Panel a, a close-up view
of those amino acid residues located within approximately 5
Å of atoms of the IMP. Panel b, a cartoon of potential
hydrogen bonds between the ligand and the protein, as indicated
by the dashed lines.
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Figure 4.
Fig. 4. Superposition of the CPS allosteric binding
pockets with bound IMP or glutamine/inorganic phosphate. The
model described in this report is shown in black, whereas the
structure of CPS complexed with glutamine and inorganic
phosphate, as described by Thoden et al. (2), is displayed in
red. Note the nearly exact correspondence between the inorganic
phosphate and the phosphoryl moiety of the nucleotide.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(1999,
274,
22502-22507)
copyright 1999.
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