Haem-Based Sensors: A Still Growing Old Superfamily - Advances in Microbial Physiology - page 30

they all rely on the haem-group reactivity (i.e. the binding of a ligand or the
change in the redox state of the iron) and translate them in a usable signal for
the transmitter domain.
Some of these sensors are better characterized (e.g. HemAT and FixL)
both structurally and functionally, where some others are not, due to protein
instability, technical complexities, or recent identification (e.g. Af GcHK,
Bpe GReg, and tGCSs).
We have also reported a recently identified class of chimeric proteins that
do not bind the haem. These non-haem-binding sensors are an excellent
example of the inventiveness of nature and of the plasticity of the globin
domain. Despite the absence of the haem group that makes it impossible
to sense gases or transfer electrons, they still function as sensors. However,
it is not yet clear what the signal is and how it is received.
The scientific community is probably still far from having an exhaustive
idea of the whole complexity of the haem-based sensor superfamily,
considering that new members are identified regularly. The bioinformatic
tools, coupled to the increasing number of sequenced genomes, provide a
powerful means for predicting more and more molecules. Physical and bio-
physical techniques are also extremely efficient for structural-functional
investigation. Nonetheless, we feel that a bigger effort should be made in order
to unravel the biological roles of these exciting molecules. Too little is known
about the pathways they control and, especially, about the receivers of
their messages.
ACKNOWLEDGEMENT
FG is a Ph.D. fellow of the Fund for Scientific Research (FWO). The support of the
University of Antwerp (GOA BOF UA 2011-2014) is acknowledged.
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