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PDBsum entry 1zfj
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Oxidoreductase
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PDB id
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1zfj
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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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Characteristics and crystal structure of bacterial inosine-5'-Monophosphate dehydrogenase.
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Authors
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R.Zhang,
G.Evans,
F.J.Rotella,
E.M.Westbrook,
D.Beno,
E.Huberman,
A.Joachimiak,
F.R.Collart.
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Ref.
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Biochemistry, 1999,
38,
4691-4700.
[DOI no: ]
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PubMed id
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Abstract
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IMP dehydrogenase (IMPDH) is an essential enzyme that catalyzes the first step
unique to GTP synthesis. To provide a basis for the evaluation of IMPDH
inhibitors as antimicrobial agents, we have expressed and characterized IMPDH
from the pathogenic bacterium Streptococcus pyogenes. Our results show that the
biochemical and kinetic characteristics of S. pyogenes IMPDH are similar to
other bacterial IMPDH enzymes. However, the lack of sensitivity to mycophenolic
acid and the Km for NAD (1180 microM) exemplify some of the differences between
the bacterial and mammalian IMPDH enzymes, making it an attractive target for
antimicrobial agents. To evaluate the basis for these differences, we determined
the crystal structure of the bacterial enzyme at 1.9 A with substrate bound in
the catalytic site. The structure was determined using
selenomethionine-substituted protein and multiwavelength anomalous (MAD)
analysis of data obtained with synchrotron radiation from the undulator beamline
(19ID) of the Structural Biology Center at Argonne's Advanced Photon Source. S.
pyogenes IMPDH is a tetramer with its four subunits related by a
crystallographic 4-fold axis. The protein is composed of two domains: a TIM
barrel domain that embodies the catalytic framework and a cystathione
beta-synthase (CBS) dimer domain of so far unknown function. Using information
provided by sequence alignments and the crystal structure, we prepared several
site-specific mutants to examine the role of various active site regions in
catalysis. These variants implicate the active site flap as an essential
catalytic element and indicate there are significant differences in the
catalytic environment of bacterial and mammalian IMPDH enzymes. Comparison of
the structure of bacterial IMPDH with the known partial structures from
eukaryotic organisms will provide an explanation of their distinct properties
and contribute to the design of specific bacterial IMPDH inhibitors.
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