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PDBsum entry 2put
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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 crystal and solution studies of glucosamine-6-Phosphate synthase from candida albicans.
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Authors
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J.Raczynska,
J.Olchowy,
P.V.Konariev,
D.I.Svergun,
S.Milewski,
W.Rypniewski.
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Ref.
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J Mol Biol, 2007,
372,
672-688.
[DOI no: ]
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PubMed id
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Abstract
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Glucosamine 6-phosphate (GlcN-6-P) synthase is an ubiquitous enzyme that
catalyses the first committed step in the reaction pathway that leads to
formation of uridine 5'-diphospho-N-acetyl-D-glucosamine (UDP-GlcNAc), a
precursor of macromolecules that contain amino sugars. Despite sequence
similarities, the enzyme in eukaryotes is tetrameric, whereas in prokaryotes it
is a dimer. The activity of eukaryotic GlcN-6-P synthase (known as Gfa1p) is
regulated by feedback inhibition by UDP-GlcNAc, the end product of the reaction
pathway, whereas in prokaryotes the GlcN-6-P synthase (known as GlmS) is not
regulated at the post-translational level. In bacteria and fungi the enzyme is
essential for cell wall synthesis. In human the enzyme is a mediator of insulin
resistance. For these reasons, Gfa1p is a target in anti-fungal chemotherapy and
in therapeutics for type-2 diabetes. The crystal structure of the Gfa1p
isomerase domain from Candida albicans has been analysed in complex with the
allosteric inhibitor UDP-GlcNAc and in the presence of glucose 6-phosphate,
fructose 6-phosphate and an analogue of the reaction intermediate,
2-amino-2-deoxy-d-mannitol 6-phosphate (ADMP). A solution structure of the
native Gfa1p has been deduced using small-angle X-ray scattering (SAXS). The
tetrameric Gfa1p can be described as a dimer of dimers, with each half similar
to the related enzyme from Escherichia coli. The core of the protein consists of
the isomerase domains. UDP-GlcNAc binds, together with a metal cation, in a
well-defined pocket on the surface of the isomerase domain. The residues
responsible for tetramerisation and for binding UDP-GlcNAc are conserved only
among eukaryotic sequences. Comparison with the previously studied GlmS from E.
coli reveals differences as well as similarities in the isomerase active site.
This study of Gfa1p focuses on the features that distinguish it from the
prokaryotic homologue in terms of quaternary structure, control of the enzymatic
activity and details of the isomerase active site.
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Figure 8.
Figure 8. Schematic representation of ligands interactions
with: (a) Glc-6-P closed form, (b) Glc-6-P/Fru-6-P open form,
(c) ADMP. Contacts present in all chains are depicted as black
broken lines and those present only in some of the chains are
shown as light grey lines. For comparison with the
protein–ligand interactions in E.
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Figure 9.
Figure 9. (a) The UDP-GlcNAc and the metal cation (blue)
bound to ISOM. A pocket in the protein surface is visible and it
accommodates the uracil ring. The ribose moiety and the
phosphate groups also interact with the protein whereas the
glucosamine moiety extends to the solvent. The 2F[o]-F[c]
electron density map is contoured at 1σ level. (b) Details of
the UDP-GlcNAc binding to ISOM. Hydrogen bonds between
UDP-GlcNAc and the protein are shown as black broken lines and
the interactions of the metal ion (blue sphere) are shown in
grey. (c) Superposition of ISOM with bound UDP-GlcNAc (protein
in red, ligand in green), ISOM without the inhibitor (yellow)
and GlmS ISOM (blue). The largest conformational change
associated with UDP-GlcNAc binding is in the position of the
Trp388 residue.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2007,
372,
672-688)
copyright 2007.
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Secondary reference #1
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Title
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Crystallization and preliminary X-Ray analysis of the isomerase domain of glucosamine-6-Phosphate synthase from candida albicans.
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Authors
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J.Olchowy,
R.Jedrzejczak,
S.Milewski,
W.Rypniewski.
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Ref.
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Acta Crystallogr Sect F Struct Biol Cryst Commun, 2005,
61,
994-996.
[DOI no: ]
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PubMed id
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Figure 1.
Crystals of the isomerase domain of GlcN-6-P synthase Acta
Crystallogr Sect F Struct Biol Cryst Commun. 2005 November 1;
61(Pt 11): 994–996. Published online 2005 October 20. doi:
10.1107/S174430910503318X. Copyright [copyright] International
Union of Crystallography 2005
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Figure 2.
A tetramer of isomerase domains of the GlcN-6-P synthase
obtained as the result of molecular replacement performed with
the homologous domain of the E. coli synthase (Teplyakov et al.,
1998[triangle]) as the search model. The monomers associate
pairwise, as in the bacterial dimer. Two such symmetry-related
dimers (shown in different colours) associate back-to-back in
the C. albicans crystal structure. The N--termini of the
polypeptide chains are indicated. The inset in the bottom right
corner shows an [alpha]-helical fragment of the electron density
after the density-modification procedure, as described in the
text. The map was contoured at the level of one root-mean-square
deviation. Acta Crystallogr Sect F Struct Biol Cryst Commun.
2005 November 1; 61(Pt 11): 994–996. Published online 2005
October 20. doi: 10.1107/S174430910503318X. Copyright
[copyright] International Union of Crystallography 2005
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The above figures are
reproduced from the cited reference
which is an Open Access publication published by the IUCr
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