Biology Reference
In-Depth Information
Abstract
A bioinformatics survey of about 120 protist and 240 fungal genomes and trans-
criptomes revealed a broad array of globins, representing five of the eight subfamilies
identified in bacteria. Most conspicuous is the absence of protoglobins and globin-
coupled sensors, except for a two-domain globin in Leishmanias, that comprises a
nucleotidyl cyclase domain, and the virtual absence of truncated group 3 globins. In
contrast to bacteria, co-occurrence of more than two globin subfamilies appears to
be rare in protists. Although globins were lacking in the Apicomplexa and the Micro-
sporidia intracellular pathogens, they occurred in the pathogenic Trypanosomatidae,
Stramenopiles and certain fungi. Flavohaemoglobins (FHbs) and related single-domain
globins occur across the protist groups. Fungi are unique in having FHbs co-occurring
with sensor single-domain globins (SSDgbs). Obligately biotrophic fungi covered in our
analysis lack globins. Furthermore, SSDgbs occur only in a heterolobosean amoeba,
Naegleria and the stramenopile Hyphochytrium. Of the three subfamilies of truncated
Mb-fold globins, TrHb1s appear to be the most widespread, occurring as multiple copies
in chlorophyte and ciliophora genomes, many as multidomain proteins. Although the
ciliates appear to have only TrHb1s, the chlorophytes have Mb-like globins and TrHb2s,
both closely related to the corresponding plant globins. The presently available number
of protist genomes is inadequate to provide a definitive census of their globins. Bayesian
molecular analyses of single-domain 3/3 Mb-fold globins suggest a close relationship
of chlorophyte and haptophyte globins, including choanoflagellate and Capsaspora
globins to land plant symbiotic and non-symbiotic haemoglobins and to vertebrate
neuroglobins.
ABBREVIATIONS
Adgb
androglobin
AGN
Agnathan, jawless vertebrates
Cygb
cytoglobin
FHb
flavohaemoglobin; N-terminal 3/3 globin linked covalently to a ferredoxin-NAD(P)H
reductase-like domain
GbX
globin X, found in fish, amphibians and gnathostomes
GbY
globin Y, found in amphibians
GCS
globin-coupled sensor; N-terminal 3/3 globin linked covalently to a gene-regulating
or methyl-accepting chemotaxis domain
Hb
haemoglobin
LECA
last eukaryote common ancestor
Ma
million years ago
Mb
myoglobin
ML
maximum likelihood
Ngb
neuroglobin
NJ
neighbour-joining
Pgb
protoglobin; single-domain 3/3 globin related to the N-terminal of GCSs