J Bacteriol, March 1998, p. 1119-1128, Vol. 180, No. 5
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Department of Molecular Biology and
Biotechnology,
Received 4 September 1997/Accepted 17 December 1997
Helicobacter pylori, a major cause of human gastric
disease, is a microaerophilic bacterium that contains neither pyruvate nor 2-oxoglutarate dehydrogenase activity. Previous studies (N. J. Hughes, P. A. Chalk, C. L. Clayton, and D. J. Kelly, J. Bacteriol. 177:3953-3959, 1995) have indicated that the major routes
for the generation of acetyl coenzyme A (acetyl-CoA) and
succinyl-CoA are via pyruvate:flavodoxin oxidoreductase (POR) and
2-oxoglutarate:acceptor oxidoreductase (OOR), respectively. The
purified POR is a heterotetrameric protein, with subunits of
48 (PorA), 36 (PorB), 24 (PorC), and 14 (PorD) kDa. In this study OOR
has been purified, and it is similarly composed of
polypeptides of 43 (OorA), 33 (OorB), 24 (OorC), and 10 (OorD) kDa.
Both POR and OOR are oxygen labile and are likely to be major
contributors to the microaerophilic phenotype of H. pylori. Unlike POR, OOR was unable to use a previously identified
flavodoxin (FldA) as an electron acceptor. Although the purified
enzymes were unable to reduce NAD(P), electrons from both pyruvate and
2-oxoglutarate could reduce NADP in cell extracts, consistent with a
role for these oxidoreductases in the provision of NADPH as a
respiratory electron donor. The H. pylori por,
oor, and fldA genes were cloned and sequenced.
The deduced por gene products showed significant sequence
similarity to archaeal four-subunit 2-oxoacid:acceptor
oxidoreductases. However, the amino acid sequences of OorA and
-B were more closely related to that of the two-subunit POR of
the aerobic halophile Halobacterium halobium. Both
porD and oorD encode integral ferredoxin-like
subunits. POR and OOR are probably essential enzymes in H. pylori, as insertion inactivation of porB and
oorA appeared to be lethal.
*
Corresponding author. Mailing address: Department of
Molecular Biology and Biotechnology, University of Sheffield, P.O. Box 594, Firth Court, Western Bank, Sheffield S10 2TN, United Kingdom. Phone: 44 114 222 4414. Fax: 44 114 272 8697. E-mail:
d.kelly{at}sheffield.ac.uk.
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