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Journal of Bacteriology, January 2001, p. 490-499, Vol. 183, No. 2
Department of Biology, Georgia State
University, Atlanta, Georgia 30303
Received 1 September 2000/Accepted 30 October 2000
The NAD+-dependent glutamate dehydrogenase (NAD-GDH)
from Pseudomonas aeruginosa PAO1 was purified, and its
amino-terminal amino acid sequence was determined. This sequence
information was used in identifying and cloning the encoding
gdhB gene and its flanking regions. The molecular mass
predicted from the derived sequence for the encoded NAD-GDH was 182.6 kDa, in close agreement with that determined from sodium dodecyl
sulfate-polyacrylamide gel electrophoresis of the purified enzyme (180 kDa). Cross-linking studies established that the native NAD-GDH is a
tetramer of equal subunits. Comparison of the derived amino acid
sequence of NAD-GDH from P. aeruginosa with the GenBank
database showed the highest homology with hypothetical
polypeptides from Pseudomonas putida, Mycobacterium
tuberculosis, Rickettsia prowazakii, Legionella pneumophila, Vibrio cholerae, Shewanella
putrefaciens, Sinorhizobium meliloti, and
Caulobacter crescentus. A moderate degree of homology, primarily in the central domain, was observed with the smaller tetrameric NAD-GDH (protomeric mass of 110 kDa) from
Saccharomyces cerevisiae or Neurospora crassa.
Comparison with the yet smaller hexameric GDH (protomeric mass of 48 to
55 kDa) of other prokaryotes yielded a low degree of homology that was
limited to residues important for binding of substrates and for
catalytic function. NAD-GDH was induced 27-fold by exogenous arginine
and only 3-fold by exogenous glutamate. Primer extension experiments
established that transcription of gdhB is initiated from an
arginine-inducible promoter and that this induction is dependent on the
arginine regulatory protein, ArgR, a member of the AraC/XyIS family of regulatory proteins. NAD-GDH was purified to homogeneity from a
recombinant strain of P. aeruginosa and
characterized. The glutamate saturation curve was sigmoid, indicating
positive cooperativity in the binding of glutamate. NAD-GDH activity
was subject to allosteric control by arginine and citrate, which
function as positive and negative effectors, respectively. Both
effectors act by influencing the affinity of the enzyme for glutamate.
NAD-GDH from this organism differs from previously characterized
enzymes with respect to structure, protomer mass, and allosteric
properties indicate that this enzyme represents a novel class of
microbial glutamate dehydrogenases.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.2.490-499.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
The gdhB Gene of Pseudomonas aeruginosa
Encodes an Arginine-Inducible NAD+-Dependent Glutamate
Dehydrogenase Which Is Subject to Allosteric Regulation
*
Corresponding author. Mailing address: College of Arts
and Sciences, Georgia State University, P. O. Box 4038, Atlanta,
GA 30302-4038. Phone: (404) 651-1410. Fax: (404) 651-4739. E-mail: aabdelal{at}gsu.edu.
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