Haem-Based Sensors: A Still Growing Old Superfamily - Advances in Microbial Physiology - page 4

Figure 1.1 Functional classification of the haem-based sensors. The organization of the
scheme is made according to the transmitter domain function. The subgroup division is
consistent with the classification illustrated in this review. Along with the complete list
of the symbols used, the appropriate name of the designated domain is also given. For
the haem-binding domains, the presence of the haem group is given as implied. Only in
the case of the numerous PAS domain, a small circle inside the graphical symbol indi-
cates the bounded haem group.
Depending on the activity of the transmitter domain, the haem-based sen-
sors can be subdivided into (i) aerotactic sensors, having a methyl-accepting
chemotaxis domain (MCP), (ii) gene-regulating sensors, (iii) sensors with an
enzymatic function, and (iv) sensors with a yet-uncharacterized function
( Fig. 1.1 ). The haem-based sensors that regulate gene expression can exercise
their function via (a) direct DNA binding, (b) protein-protein interaction, or
(c) biosynthesis of a second messenger.
2.1. Haem-based sensors with aerotactic function
The aerotactic sensors are responsible for sensing the intracellular O 2 con-
centration and delivering the signal to the downstream transduction cascade.
The result is that the flagella motor is influenced, thus the swimming