Background: Hemoglobin (Hb) subunits are composed of the specific functional prosthetic
group “heme’’ and a protein moiety “globin”. Bird Hbs are functionally similar to mammalian
Hbs but they are structurally dissimilar with mammalian. The insufficient structural studies on
avian Hbs limit us to understand their degree of adaptation to such critical environments. The Great
Cormorant (GCT) can fly and swim, the dual characteristic of GCT leads to study the sturcture of
Objective: To determine the crystal structure of Great Cormorant Hemoglobin and to compare its
three dimensional structure with other high and low oxygen affinity hemoglobin species to understand
its characteristic features of high oxygen affinity.
Method: The GCT hemoglobin has been purified, crystallized and data sets were processed using
iMosflm. The integrated data has been solved using Molecular replacement method using Graylag
hemoglobin (1FAW) as the template. The structure has been deposited in Protein Data Bank with
PDB code: 3WR1.
Results: In order to characterize the tertiary and quaternary structural differences, the structure of
cormorant hemoglobin is compared with GLG, BHG and human Hb. The larger variation observed
between GCT and human Hb indicates that GCT Hb differs remarkably from human. The α1β1
interface of Great cormorant Hb is similar to bar-headed goose Hb with few amino acid substitutions.
It has been found that the interaction which is common among avian hemoglobins (α119 Pro-
β55Leu) is altered by Ala 119 in GCT. This intra-dimer contact (α119 Pro – β 55 Leu) disruption
leads to high oxygen affinity in BGH Hb. In cormorant, GLG and human the proline is unchanged
but interestingly, in cormorant Hb, the β55 position was found to be Thr instead of Leu. Similar
kind of substitutions (β 55 Leu - Ser) observed in Andean goose Hb structure leads to elevated oxygen
affinity between Hb-O2. To our surprise, such type of substitution at β 55 (Thr) in cormorant
Hb confirms that it is comparable with Andean goose Hb structure. Thus the sequence, structural
differences at alpha, beta heme pocket and interface contacts confirms that GCT adopts high oxygen
Conclusion: The three dimensional structure of Great cormorant hemoglobin has been investigated
to understand its unique structural features to adopt during hypoxia condition. By comparing the
sequence and overall structural similarities with high and low oxygen affinity species, it appears
that GCT has more possibilities to subsist with low oxygen demand.