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Bacteria can occur almost anywhere on earth and exist under the most varying
conditions. If these tiny, microscopic organisms are to survive in these environments,
they need to be able to rapidly detect changes in their surroundings and react
to them. Scientists at the Johannes
Gutenberg University of Mainz are currently investigating how bacteria manage
to pass information on their environment across their membranes into their cell
nuclei. "The sixty-four-thousand- dollar question is how signals are transmitted
across the cell membrane," explains Professor Gottfried Unden of the Institute
of Microbiology and Vinology. Working in collaboration with the Max Planck Institute
for Biophysical Chemistry in Göttingen, his research group has demonstrated
that structural alterations to membrane-based sensors play a major role in the
transfer of signals.
Some bacteria possess more than 100 different sensors that they use to form
a picture of their environment. These sensors can show, for example, whether
nutrient substrates and/or oxygen are present in the immediate neighborhood
of the cell and what the external status of temperature and light is like. These
sensors are mainly located in the cell membrane, i.e., the layer separating
bacteria cells from the environment. From there they then transmit signals into
the cell nucleus. Thanks to the development of new methods of isolating these
sensors and of other innovative techniques, it is now possible to discover how
all this works. The researchers in Mainz have also managed to modify a sensor
that detects an important bacterial substrate so that it can be analyzed making
use of new spectroscopic techniques. "This is the first time that solid-body
nuclear magnetic resonance (NMR) spectroscopy has been used to investigate large
membrane proteins," stated Professor Unden. In addition to this functional
analysis, the structural analysis undertaken by the biophysicist team in Göttingen
headed by Professor Marc Baldus has identified important details of the signal
transmission process: a stimulus molecule – carbonic acid in this case
– binds to a part of the sensor that protrudes from the cell. This appears
to result in dissolution of the ordered structure of that segment of the sensor
within the cell that is in non-stimulated status. It seems that it is this plasticity
that elicits the subsequent activation of the enzymatic reaction cascade within
the cell. This results in the cellular response, which, for example, can take
the form of neosynthesis of enzymes or the development of protective mechanisms.
In addition to the new findings on signal transmission published in Nature
Structural and Molecular Biology, the microbiologists of Mainz University have
discovered a previously unknown and exceptional method of signal detection employed
by the same sensor (designated DcuS), which they discuss in an article in the
Journal of Biological Chemistry. This shows that bacteria react not only to
their extracellular environment, but also to the intracellular situation. It
is becoming apparent that it is not the sensors alone that detect stimuli. A
second stimulus detection pathway is represented by the transport system that
channels substrates into the cell. Once the substrate – carbonic acid
– has been taken up, the transporter notifies the sensor of this. Prof.
Unden added, "We have been able to identify that segment of the transporter
that is responsible for the control of sensor functioning. The transporter is
of fundamental importance for the function of the sensor. Without the transporter,
the sensor does not work correctly and is constantly in activated status,"
explained Professor Unden, who suspects that this function-related feedback
on metabolic and transport activity is often more important for a cell than
information concerning concentrations only.
Posted January 15th, 2009
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