Nucleotide and
protein sequences exhibiting high similarity to land plant non-symbiotic
hemoglobins (nsHbs) were identified in the genome of the prasinophyceae algae Micromonas pusilla, M. sp. RCC299, and Ostreococcus
sp. RCC809. Sequence alignment showed that Micromonas
and Ostreococcus nsHb-like globins
(Micropusil, Microsp, and Ostreosp nsHbs, respectively) contain the highly
conserved Phe B10, Phe CD1, and proximal and distal His in identical positions
as in land plant nsHbs. Also, phenetic analysis showed that Micromonas and Ostreococcus nsHb-like globins are closely related to bacterial Hbs
and closer to bryophyte than to other land plant nsHbs. This observation
suggests that Micromonas and Ostreococcus nsHb-like globins evolved
from a bacterial Hb and are ancestral to land plant nsHbs. Modeling of the
tertiary structure of Micromonas and Ostreococcus nsHb-like globins showed
that these proteins could fold into the canonical 3-on-3 myoglobin-fold. Also,
analysis of the distance of distal His to the heme-Fe suggests that predicted
Micropusil and Ostreosp nsHbs might be pentacoordinate and that the Microsp
nsHb might be hexacoordinate.