Biology Reference
In-Depth Information
metazoans, the single-domain globins, and the flavohemoglobins; (ii) the
3/3 globins of bacteria (GCSs) and the protoglobins; and (iii) the 2/2 glo-
bins. Given that all the three globin subgroups occur only in Bacteria, it has
been proposed that globins initially appeared and evolved in these organisms
(
Vinogradov et al., 2005, 2006
). Subsequently, via lateral gene transfers
(LGTs), they spread in Archaea and Eukarya, starting the evolutionary pro-
cess that resulted in the globins we are studying these days (
Moens et al.,
1996; Vinogradov et al., 2007
).
Concerning the formation of chimeric globins, that is, the GCSs, the
evolutionary process is schematically divided into three steps: (1) after the
emergence of the first 3/3 single-domain and soluble globin ancestor in
LUCA, the 2/2 globins evolved and diverged; (2) then alternative domains
fused to the 3/3 globins, as such producing the first chimeric GCSs; (3) as
last, two sorts of LGTs took place, one between Bacteria and the eukaryote
precursor(s), and the other between Bacteria and Archaea (
Vinogradov
et al., 2007
).
It can be hypothesized that the evolution of the haem-based sensors hap-
pened similarly. That is, the initial emergence of the simple single domain
proteins was followed by their covalent connection and, therefore, the for-
mation of chimeric functional sensors with precise functions.
4. CONCLUSIONS AND FUTURE PERSPECTIVES
The haem-based sensor superfamily comprises numerous chimeric
proteins present in Bacteria, Archaea, and Eukarya. Supposedly, they
evolved as single domain proteins, which fused to each other afterwards.
The haem-based sensors' evolutionary driving force is the need of the organ-
isms and cells to link intra- and extracellular changes with intracellular
response. As such, they contain a sensor domain that detects a specific signal
and, via structural rearrangements, activates or inactivates the cognate trans-
mitter domain. This mechanism provides a fine tuning of the biochemical
reactions, resulting in adapted intracellular modifications.
The haem-based sensors can be classified on the basis of the architecture
of the haem-binding domain or on the function of the transmitter domain.
In this review, we support the functional classification; therefore we divided
the sensors into (i) aerotactic; (ii) gene regulating via protein-DNA interac-
tion, protein-protein interaction, or second messenger biosynthesis;
(iii) enzymatic function; and (iv) unknown function. All these subgroups
emphasize the extreme flexibility of the haem-binding domains. Indeed,
