Affiliation:
1. Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, USA
Abstract
ABSTRACT
In
Mycobacterium tuberculosis
, the stringent response to amino acid starvation is mediated by the
M. tuberculosis
Rel (Rel
Mtb
) enzyme, which transfers a pyrophosphate from ATP to GDP or GTP to synthesize ppGpp and pppGpp, respectively. (p)ppGpp then influences numerous metabolic processes. Rel
Mtb
also encodes a second, distinct catalytic domain that hydrolyzes (p)ppGpp into pyrophosphate and GDP or GTP. Rel
Mtb
is required for chronic
M. tuberculosis
infection in mice; however, it is unknown which catalytic activity of Rel
Mtb
mediates pathogenesis and whether (p)ppGpp itself is necessary. In order to individually investigate the roles of (p)ppGpp synthesis and hydrolysis during
M. tuberculosis
pathogenesis, we generated Rel
Mtb
point mutants that were either synthetase dead (Rel
Mtb
H344Y
) or hydrolase dead (Rel
Mtb
H80A
).
M. tuberculosis
strains expressing the synthetase-dead Rel
Mtb
H344Y
mutant did not persist in mice, demonstrating that the Rel
Mtb
(p)ppGpp synthetase activity is required for maintaining bacterial titers during chronic infection. Deletion of a second predicted (p)ppGpp synthetase had no effect on pathogenesis, demonstrating that Rel
Mtb
was the major contributor to (p)ppGpp production during infection. Interestingly, expression of an allele encoding the hydrolase-dead Rel
Mtb
mutant, Rel
Mtb
H80A
, that is incapable of hydrolyzing (p)ppGpp but still able to synthesize (p)ppGpp decreased the growth rate of
M. tuberculosis
and changed the colony morphology of the bacteria. In addition, Rel
Mtb
H80A
expression during acute or chronic
M. tuberculosis
infection in mice was lethal to the infecting bacteria. These findings highlight a distinct role for Rel
Mtb
-mediated (p)ppGpp hydrolysis that is essential for
M. tuberculosis
pathogenesis.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
73 articles.
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