Biology Reference
In-Depth Information
from the globins we associatewithmammalian oxygen transport?', and 'What
function do they provide for the cells inwhich they are expressed?' To restate
the issues in plain terms, 'How common are these globins, what do they look
like, andwhat do they do?' Themost progress has beenmade in addressing the
first point, or the commonality of globins in these microbes. The advent of
genomic sequencing since 1992 has provided substantial amounts of
phylogenetic information on globins from photosynthetic microbes, with
additional sequences becoming available at an accelerated pace. From this,
researchers have identified the ancient origins of globins, traced their evolu-
tion and even begun to illuminate the evolution of eukaryotic photosynthetic
cells through the phylogenetic linkage among cyanobacterial globins and
their counterparts in algae and higher plants. These investigations will no
doubt continue, and with an ever-more complete genetic picture of both
cyanobacteria and algae, our understanding of their phylogenetic heritage
will grow. But we must begin to balance this wealth of genomic knowledge
with substantive information about the actual proteins.
6.1. Physiological studies
A physiological understanding of globin function within photosynthetic
organisms such as cyanobacteria and green algae presents a true opportunity.
The functional characterization of the GlbN protein in
Synechococcus
sp.
PCC 7002 (
Scott et al., 2010
) demonstrates that such studies can help define
the role of globins within these systems. Below is a 'wish list' of studies
involving both cyanobacterial and algal species. All of these studies are based
upon currently available techniques but will nonetheless be challenging. As
discussed in
Section 5
, the functions of globins are most likely tied to dio-
xygen manipulation and reactive molecule processing. As discussed in
Section 3
, photosynthetic organisms are ripe with oxygen evolution, reac-
tive molecule formation and electron transfer. They are also masters at
adapting to diverse environments and conditions.
Section 4
has shown tan-
talizing clues that genes for globins are regulated in response to these molec-
ular events within photosynthetic cells. The challenge, therefore, is left for us
to design and implement experiments that can effectively link the function
of globins to the dynamic physiology occurring within actively photo-
synthesizing organisms.
6.1.1 Purification of globins from the source organisms
Specificity for the haem cofactor is a relatively unexplored aspect of globins in
photosynthetic organisms. Spermwhale apomyoglobin binds chlorophyll-like
