Microbial Eukaryote Globins - Advances in Microbial Physiology - page 393

(Ngbs) and cytoglobins (Cygb), and others with more limited distribution,
such as globin X (GbX) and globin Y (GbY), the avian eye-specific globin E
(GbE), and the recently discovered chimeric androglobin, present in most
deuterostomes, several protostomes, more basal animal clades and in
choanoflagellates ( Hoogewijs, Ebner, et al., 2012 ). These are all 3/3 globins
as are almost all the metazoan globins. Because of the sequence similarity
between vertebrate globins such as Mb, Ngb and Cygb on one hand,
and the bacterial SDgbs and FHbs on the other ( Vinogradov, 2008 ), we
proposed subsuming the FHb family into the M family (for myoglobin-like),
which would therefore encompass all 3/3 eukaryote globins, including
all the 3/3 globins of vertebrates, other metazoans, plants and protists.
For the bacterial GCS family, we propose S for sensor family, retaining
GCS for the chimeric members and using SSDgb for the related single-
domain sensor globins. The three classes of the T family are TrHb1s, TrHb2s
and TrHb3s. In bacteria these are also sometimes called N, O and
P, respectively.

4. MICROBIAL EUKARYOTE GLOBINS
Table 9.3 summarizes the globin subfamilies identified in approxi-
mately 120 protist genomes and transcriptomes. A detailed list of protist glo-
bins is available as Supplementary Table S1 at http://www.elsevierdirect.
com/companions/9780124076938 . A diagrammatic view of protist diver-
sity and the globin subfamilies found in protist genomes are shown
in Fig. 9.1 .In Table 9.3 , we also include the globins found in opisthokonts
other than metazoans and fungi, namely choanoflagellates

and ichtyosporeans.

4.1. Archaeplastida
The Archaeplastida (Viridiplantae in Table 9.3 ) are represented by
14 chlorophyte genomes, all of which contain globins, TrHb1s, TrHb2s
and SDgbs. The chlorophyceans Coccomyxa subellipsoides and Chlorella
variabilis have only TrHb1s and TrHb2s. A chimeric 587-residue TrHb1
in C . subellipsoides has an N-terminal domain identified as a member of
the bestrophin family (PFAM01062), transmembrane proteins that share
an RFP (Arg-Phe-Pro) motif and are thought to function as chloride chan-
nels ( Hartzell, Qu, Yu, Xiao, & Chien, 2008 ).