Biology Reference
In-Depth Information
cnidarians and poriferans. Although the node probabilities remain low, it is
worth noting the following: (1) The vertebrate globin phylogeny is pre-
served (boxes labelled HbB, HbA, Mb, GbY, AGN, Cygb, GbX and
Ngb). (2) Most of the protist globins are clearly separated from higher
eukaryote globins. (3) The proximity of plant Hbs to vertebrate Ngbs with
the insertion of chlorophyte, haptophyte and sea-urchin (ECHI1) globins
between the latter. (4) The proximity of choanoflagellate (CHOA) and stra-
menopile (STR) to the plant Hbs. (5) The grouping of echinodermHbs into
two groups, one next to Ngbs (box ECHI1), and another, vicinal to Cygbs
(ECHI2). A number of lower eukaryote globins cluster either with the Ngbs
and GbXs, or with the Cygbs, implying the presence of at least two distinct
globin lineages in the lower eukaryotes, one related to Ngbs and the other to
Cygbs. Notable is the clustering of cnidarian globins with the GbX lineage.
The latter result agrees with the recent observations by
Blank and Burmester
(2012)
. Furthermore, there is the clustering (though only with 0.85 support
value) of the multidomain
Leishmania
chimeric globin with the GbX clade.
Our results suggest that opisthokont SDgbs are probably related to the Ngb
clade. Obviously, much work remains to be done.
6. GLOBIN FUNCTION
6.1. Overview of globin functions
It has become abundantly clear over the last two decades that Hbs have func-
tions other than oxygen storage and transport, which are probably limited to
multicellular organisms in which oxygen must be transported over greater dis-
tances (
Vinogradov & Moens, 2008
). However, we should not forget that
physiologically significant gradients of oxygen exist even in prokaryotic cells
(see, however,
Unden et al., 1995
) and that oxygen-binding proteins may play
key roles in oxygen delivery and storage. For example, there is a vast literature
detailing the beneficial effects of heterologous expression of the
Vitreoscilla
glo-
bin (Vgb, VHb) on growth, metabolism and product yields (reviewed by
Frey, Shepherd, Jokipii-Lukkari, Haggman, & Kallio, 2011
). These effects
Figure 9.9—Cont'd posterior probabilities (
>
0.5). Each sequence is identified by the
first three letters of the binomial, number of residues, the first three or four letters of
the taxon and the identification number. Abbreviations: AGN, Agnathan, jawless verte-
brates; ALV, Alveolate; AMO, Amoebozoa; CEPH, Cephalochordate; CHL, Chlorophyte;
CHOA, Choanoflagellate; CNI, Cnidaria; ECHI, Echinoderm; EUG, Euglenozoa; FIL,
Filasterea; HEMI, Hemichordate; ICH, Ichtyosporea; POR, Porifera; RHO, Rhodophyte;
STR, Stramenopile; URO, Urochordate.
