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Journal of Bacteriology, December 2000, p. 6679-6686, Vol. 182, No. 23
Department of Biochemistry, Albert Einstein
College of Medicine, Bronx, New York 10461
Received 19 June 2000/Accepted 18 September 2000
Legionella pneumophila, the causative organism of
Legionnaires' pneumonia, contains two enzymes with catalatic and
peroxidatic activity, KatA and KatB. To address the issue of redundant,
overlapping, or discrete in vivo functions of highly homologous
catalase-peroxidases, the gene for katA was cloned and its
function was studied in L. pneumophila and
Escherichia coli and compared with prior studies of
katB in this laboratory. katA is induced during
exponential growth and is the predominant peroxidase in stationary
phase. When katA is inactivated, L. pneumophila
is more sensitive to exogenous hydrogen peroxide and less virulent in
the THP-1 macrophage cell line, similar to katB.
Catalatic-peroxidatic activity with different peroxidatic cosubstrates
is comparable for KatA and KatB, but KatA is five times more active
towards dianisidine. In contrast with these examples of redundant or
overlapping function, stationary-phase survival is decreased by 100- to
10,000-fold when katA is inactivated, while no change from
wild type is seen for the katB null. The principal clue for
understanding this discrete in vivo function was the demonstration that
KatA is periplasmic and KatB is cytosolic. This stationary-phase
phenotype suggests that targets sensitive to hydrogen peroxide are
present outside the cytosol in stationary phase or that the peroxidatic
activity of KatA is critical for stationary-phase redox reactions in
the periplasm, perhaps disulfide bond formation. Since
starvation-induced stationary phase is a prerequisite to acquisition of
virulence by L. pneumophila, further studies on the
function and regulation of katA in stationary phase may
give insights on the mechanisms of infectivity of this pathogen.
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Catalase-Peroxidases of Legionella
pneumophila: Cloning of the katA Gene and Studies
of KatA Function
*
Corresponding author. Mailing address: Department of
Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park
Avenue, Bronx, NY 10461. Phone: (718) 430-3010. Fax: (718) 430-8565. E-mail: steinman{at}aecom.yu.edu.
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