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PDBsum entry 1a3a
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Phosphotransferase
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PDB id
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1a3a
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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 structure of the escherichia coli phosphotransferase iiamannitol reveals a novel fold with two conformations of the active site.
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Authors
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R.L.Van montfort,
T.Pijning,
K.H.Kalk,
I.Hangyi,
M.L.Kouwijzer,
G.T.Robillard,
B.W.Dijkstra.
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Ref.
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Structure, 1998,
6,
377-388.
[DOI no: ]
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PubMed id
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Abstract
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BACKGROUND: The bacterial phosphoenolpyruvate-dependent phosphotransferase
system (PTS) catalyses the cellular uptake and subsequent phosphorylation of
carbohydrates. Moreover, the PTS plays a crucial role in the global regulation
of various metabolic pathways. The PTS consists of two general proteins, enzyme
I and the histidine-containing protein (HPr), and the carbohydrate-specific
enzyme II (EII). EIIs are usually composed of two cytoplasmic domains, IIA and
IIB, and a transmembrane domain, IIC. The IIA domains catalyse the transfer of a
phosphoryl group from HPr to IIB, which phosphorylates the transported
carbohydrate. Knowledge of the structures of the IIA proteins may provide
insight into the mechanisms by which the PTS couples phosphorylation reactions
with carbohydrate specificity. RESULTS: We have determined the crystal structure
of the Escherichia coli mannitol-specific IIA domain, IIAmtl (M(r) 16.3 kDa), by
multiple anomalous dispersion analysis of a selenomethionine variant of IIAmtl.
The structure was refined at 1.8 A resolution to an R factor of 19.0% (Rfree
24.2%). The enzyme consists of a single five-stranded mixed beta sheet, flanked
by helices on both sides. The phosphorylation site (His65) is located at the end
of the third beta strand, in a shallow crevice lined with hydrophobic residues.
The sidechains of two conserved active-site residues, Arg49 and His111, adopt
two different conformations in the four independent IIAmtl molecules. Using a
solution structure of phosphorylated HPr, and a combination of molecular
modelling and NMR binding experiments, structural models of the HPr-IIAmtl
complex were generated. CONCLUSIONS: The fold of IIAmtl is completely different
from the structures of other IIA proteins determined so far. The two
conformations of Arg49 and His111 might represent different states of the active
site, required for the different phosphoryl transfer reactions in which IIAmtl
is involved. A comparison of the HPr-IIAmtl model with models of HPr in complex
with other IIA enzymes shows that the overall interaction mode between the two
proteins is similar. Differences in the stabilisation of the invariant residue
Arg17 of HPr by the different IIA proteins might be part of a subtle mechanism
to control the hierarchy of carbohydrate utilisation by the bacterium.
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Figure 4.
Figure 4. The structure of IIA^mtl. (a) Stereo Ca trace of
IIA^mtl, molecule A[I], with N and C termini and every tenth
residue labelled. (b) Ribbon stereo view of the structure of
IIA^mtl, molecule A[I], generated using the program MOLSCRIPT
[49]. Strands are shown in red, helices in yellow and loops in
light yellow. The catalytic His65 is shown in a ball and stick
representation. Also shown are the conserved Arg49 and His111.
The N and C termini are indicated. See also Kinemage
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The above figure is
reprinted
by permission from Cell Press:
Structure
(1998,
6,
377-388)
copyright 1998.
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