|
Mapping
the global impact of a high-energy metabolic
intermediate
on a
signal transduction network
Derived
from acetyl-CoA, the keystone compound of central
metabolism, acetyl-P stores more energy than does ATP.
This ability forms the basis for its proposed role as a
global signal. Although the seminal studies that formed
the basis for this proposal were performed more than a
decade ago, two major questions have remained
unanswered: Does acetyl-P actually exert a global impact
upon cellular physiology? And, if so, how does it do it?
We
can now confidently answer ‘yes’ to the first
question. A few years ago, we reported the existence of
about 100 acetyl-P-sensitive genes, mostly involved in
the transition of motile individuals into sessile
biofilm communities. Now, we can report that much (but
not all) of this response acts through the two-component
signal transduction (2CST) response regulator RcsB. This
global regulator controls about 2.5% of the entire
genome, including genes that encode the enzymes that
synthesize cell surface organelles (capsule, flagella,
and type 1 pili) required for the proper development of
biofilms. Thus, we have established a role for acetyl-P
as a significant input into the network of 2CST pathways
and demonstrated definitively the existence of a direct
link from central metabolism to signal transduction.
We
also can confidently answer ‘yes’ to the second
question. Over the past two years, we have taken a
classic thin layer chromatographic assay for the
measurement of phosphorylated compounds and optimized it
for the accurate and reproducible detection of the
highly unstable acetyl-P. We can now say that the
intracellular concentration of acetyl-P rivals that of
ATP. This observation negates the major argument against
the hypothesis that acetyl-P donates phosphoryl groups
directly to certain response regulators, i.e. that the
intracellular pool of acetyl-P is too small.
Now
that we have demonstrated that acetyl-P actually
functions as a global signal and that it can do so by
donating its phosphoryl group to certain RR, we have
initiated a three-pronged research plan. We have begun a
genetics-based systems biological approach to determine
the full impact of acetyl-P on the entire network of
2CST pathways. We have begun to dissect the regulatory
mechanisms used by cells to regulate the levels of this
highly reactive global signal. Finally, we have
initiated collaborations with physical chemists (Drs.
Paul Chiarelli and David French of Loyola University
Chicago) to develop mass and NMR-based
assays to monitor acetyl-P.
|
