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Weich, & Hankeln, 2002; Trent & Hargrove, 2002
) and neuroglobin
(
Burmester, Weich, Reinhardt, & Hankeln, 2000
) made their appearance
in the vertebrate set; multiple sequences and structures for Group II and
Group III truncated globins became available (as reviewed in
Nardini,
Pesce, Milani, & Bolognesi, 2007
); and globin-coupled sensors (GCSs)
and protoglobins (Pgbs) were discovered (as reviewed in
Freitas, Saito,
Hou, & Alam, 2005
). All these developments provided context and material
for a broader understanding of the haemoglobin superfamily. The vast
increase in the number of sequenced genomes allowed Vinogradov and
colleagues to develop an exhaustive model of haemoglobin evolution
(
Vinogradov et al., 2005
) and iterate on this model ever since (
Hoogewijs
et al., 2012; Vinogradov & Moens, 2008; Vinogradov, Fernandez, et al.,
2011; Vinogradov et al., 2007, 2013
). They concluded that the
haemoglobin superfamily is composed of three lineages. The best known
includes the flavohaemoglobins (FHbs), bacterial proteins that contain an
N-terminal haem-binding domain and a flavin-binding domain, and the
single-domain globins (SDgbs), which are related to the haem domain of
the FHbs. Myoglobin belongs to this lineage. A second lineage comprises
the GCS proteins. These are also chimeric and contain an N-terminal
canonical globin domain. The single-domain Pgbs (
Hou et al., 2001
) and
sensor single-domain globins related to the GCS globin domain (SSDgbs)
fit in this family. Finally, the truncated lineage is divided into three groups
as mentioned earlier.
In light of sequence alignments and the structural information, the name
two-over-two (or 2/2) globin surfaced as an alternative name for the trun-
cated globins. This is an apt reference to the helical topology and the fact that
truncated globin domains differ considerably in length and the position of
insertions and deletions. The full-size globins exhibit a three-over-three
(or 3/3) fold and are often referred to as 3/3 globins for contrast with the
2/2 proteins. As pointed out in a recent publication (
Vinogradov et al.,
2013
), the field of haemoglobin research suffers from haphazard and evolv-
ing nomenclature. In this chapter, we follow the new recommendations
proposed in that work. The three lineages are therefore referred to as the
M family (i.e. myoglobin-like, including FHb and SDgb), the S family
(i.e. sensor, including GCS, Pgb, SSDgb), and the T family (i.e. truncated,
classified as TrHb1, TrHb2 or TrHb3 for Group I, II or III, respectively).
TrHb1s, SDgbs and SSDgbs are found in Cyanobacteria. TrHb1s outnum-
ber proteins from the M and S lineages, but as we will see, the presence of
