Biology Reference
In-Depth Information
limited. Nevertheless, it is a key part in our current understanding of the
function of these enzymes, and once coupled to additional phylogenetic
findings, it is expected to lead us to truly dramatic discoveries.
4. PHYSIOLOGICAL CHARACTERIZATION
The current state within the field of globin biology is decidedly one-
sided. In the previous section, we discussed the recent explosion of genomic
data that stretch across all kingdoms of life, giving an unparalleled view of
evolution and phylogeny at a level of detail unimaginable only a decade
ago. However, when we look at experimental data, structural analysis and
physiological analysis, we see a relative handful of examples. Without
detracting from the importance of these results, we must emphasize that a
deep and vast field of information about the function and physiological value
of globins remains virtually untapped. In a recent publication reviewing the
status of bacterial globin research, the authors bemoaned the fact that though
thousands of genomic sequences are currently available, the sum of the 'gold
standard' of globin research—functional determination by mutagenesis and
phenotypic analysis—is contained in only a few experiments (
Vinogradov
et al., 2013
). In this section, we review past and current work conducted
on cyanobacteria and algae at the physiological, proteomic and/or trans-
criptomic level. We believe that these are the bedrock experiments on
which the future understanding of globin biology will be built.
4.1. Nostoc commune
The first published discovery of a globin in cyanobacteria also contained the
first physiological hint at one of the roles of these proteins. The 1992
Science
paper by
Potts et al. (1992)
described the
glbN
gene discovered as an open
reading frame (ORF) within the
nifUHD
gene cluster of
N. commune
UTEX
584. The location of the ORF within a gene cluster dedicated to nitrogen
fixation (
Angeloni & Potts, 1994
) and the deduced amino acid similarity to
globins previously identified in ciliated protozoa
P. caudatum
(
Iwaasa et al.,
1989
) and
T. pyriformis
(
Iwaasa et al., 1990
) led to the supposition that the
gene product for the
glbN
gene is involved in nitrogen metabolism.
The resulting protein, which we call here GlbN according to the
corresponding gene, was found through immunoblotting to be expressed
only during prolonged anaerobic growth under conditions of nitrogen star-
vation. The relative expression of GlbN shows marked correlation to the
expression of both NifH and PetH proteins. NifH is a dinitrogen reductase
