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the deletion of these genes. From studies such as that of
Synechococcus
sp.
PCC 7002, we have seen that under normal growth conditions very little
difference is detected between the deletion strain and the wild-type strain
(
Scott et al., 2010
). Transcriptomic data are helpful in identifying conditions
where globin gene expression changes, revealing when cell survivability may
be enhanced by globin production. Using variations in environmental con-
ditions, the possibility for an identifiable phenotype can be investigated. The
generation of such novel strains from
C. reinhardtii
would allow the linkage
of globins to individual metabolic pathways.
6.1.3 Linkage to pathways
6.1.3.1 Nitrogen metabolism
The
Synechococcus
sp. PCC 7002 study (
Scott et al., 2010
) suggests strongly
the involvement of globins in the metabolism of nitrogen-containing com-
pounds within cyanobacteria, but many questions remain as to the true func-
tion of such proteins. One possible role for GlbN is in mitigation of
peroxynitrite, a reactive molecule present as a by-product in nitrogen
metabolism and implicated in several disease pathways (
Alvarez & Radi,
2003
). Interestingly, peroxynitrite, which results from the combination of
nitric oxide with the superoxide anion, is thought to participate in signalling
in plants through tyrosine nitration (
Vandelle & Delledonne, 2011
).
Whether peroxynitrite chemistry is relevant to globins in photosynthetic
microbes is a possibility that has not been explored.
Within eukaryotic algae, a recent paper has begun to make inroads into
understanding potential globin roles in nitrogen metabolism (
Hemschemeier
et al., 2013
). As discussed in
Section 4.5
, this study looked at the effects of
reduced protein expression (through RNA knockdown) on a TrHb1
(THB8) from the alga
C. reinhardtii
. The result was a dramatic decrease in cell
survivability during conditions of hypoxia, and this survival was linked to the
prevalence of nitric oxide. It still needs to be determined exactly how THB8
confers this survivability, and what interactions it may have with nitric oxide
within the cell, but it does signal a new and growing interest in these proteins
and their interactions with reactive nitrogen molecules.
Further study of globin function within nitrogen metabolism of cyano-
bacteria has many advantages as this metabolism is quite diverse in these
organisms. With globins present in species both with and without nitrogen
fixation pathways and both with and without nitric oxide reductases, there is
the opportunity to look at similar proteins in different contexts. This can
definitely be tied to the wealth of available structural and ligand-binding
