Biology Reference
In-Depth Information
information. By studying the nitrogen metabolism pathways in cyano-
bacteria, we have a clear route to deciphering the relationship between
structure and metabolic function. It is probable that these metabolic func-
tions will be analogous to the function of globins in other organisms, giving
insight into other pathways such as disease resistance in bacteria.
6.1.3.2 Photosynthesis
In photosynthetic organisms, extreme environmental conditions such as
high light intensities can be detrimental to the photosynthetic process
( Krieger-Liszkay, 2005 ), reducing the photosynthetic efficiency and giving
rise to deleterious by-products (e.g. superoxide radicals, singlet oxygen) and
conditions for the formation of RNS. The localization of several globins
from chlorophytes to the chloroplast, either by predicted chloroplast transit
peptide or by confirmed immuno-staining of the organelle, suggests that
these proteins are involved in mitigating the production of these molecules
as a way of preserving photosynthetic efficiency under harsh conditions. The
C. reinhardtii protein THB4 occurs in the most genetically tractable species,
and is closely related to the LI637 protein from C. eugametos ( Fig. 6.3 ) for
which some physiological information is available. This protein may be
the most promising target for understanding how these globins fit into
photosynthetic metabolism.
It will also be interesting to see how the eukaryotic globins in chloro-
plasts relate to the cyanobacterial globins in terms of function. Despite
the large evolutionary distance between the two species, the structure of
ligand-bound TrHb1 (GlbN) from Synechocystis sp. PCC 6803 ( Hoy
et al., 2004 ) is very similar to the structure of the TrHb1 (CtrHb) from
C. eugametos ( Pesce et al., 2000 ). The question becomes whether we can
draw similarities between the functions of these proteins as well. In this
sense, eukaryotic globins operating within the chloroplast are exposed to
an environment similar to that of their counterparts in cyanobacteria.
The eukaryotic globin sequences in Fig. 6.3 were analyzed by the predictive
software PredAlgo ( Tardif et al., 2012 ). Five of the eukaryotic globins do, in
fact, have predicted chloroplast targeting sequences. Of these, three are
TrHb1s (from Chlamydomonas species), one is a TrHb2 (from Chlorella
vulgaris ), and one is predicted to be an SDgb (M globin; this protein is in
Micromonas sp. RCC299). If globins in the chloroplast are used to mitigate
similar reactive molecules, then why is there such a phylogenetically diverse
group of globins
targeted to the chloroplast among different
species
of chlorophytes?
Search WWH ::




Custom Search