Recombinant Notothenia coriiceps neglecta Hemoglobin subunit alpha-2 (hba2)

Primary Sequence and Molecular Properties

The alpha chain of N. coriiceps neglecta hemoglobin (Hb1) contains 142 amino acid residues, with an acetylated serine residue at the N-terminus . Its molecular mass is 15,519 Da . Key structural features include:

• Low Homology to Non-Antarctic Fish: Sequence comparisons show reduced homology with alpha chains of other poikilothermic (cold-blooded) fish but higher homology to the bluefin tuna, a non-poisikilothermic species .

• Functional Adaptation: The hemoglobin of N. coriiceps neglecta exhibits a reduced Bohr effect, enabling efficient oxygen binding at low temperatures and high pH .

Comparative Homology

Source:

Alpha-Globin Gene Organization

In notothenioid fish, the alpha-globin gene cluster on chromosome 16 includes multiple paralogs (e.g., α-globin.1, α-globin.2) . N. coriiceps neglecta retains functional α-globin genes, whereas icefishes (Channichthyidae) lack β-globin genes entirely but retain vestigial α-globin remnants .

Evolutionary Pressures

• Cold Adaptation: The alpha chain’s sequence divergence reflects selection for low-temperature stability. For example, reduced β-globin diversity in N. coriiceps neglecta correlates with ecological specialization .

• Transposon-Mediated Expansion: Tandem duplications and TAT-like repeat insertions in hemoglobin gene clusters may influence expression regulation .

Key Studies on N. coriiceps neglecta Hemoglobin

1. Amino Acid Sequence Determination:

   • The alpha chain’s sequence was resolved via automated Edman degradation and carboxypeptidase treatment .

   • Critical residues include Glu-6 and Gln-54, which may stabilize the protein at low temperatures .

2. Functional Properties:

   • Oxygen Affinity: The hemoglobin of N. coriiceps neglecta has a high affinity for oxygen, compensating for reduced erythrocyte count in cold environments .

   • Lack of Root Effect: Unlike some Antarctic fish, N. coriiceps neglecta’s hemoglobin exhibits minimal pH-dependent oxygen release, optimizing oxygen delivery in stable pH conditions .

3. Evolutionary Insights:

   • Diversifying Selection: Phylogenetic analyses reveal elevated nonsynonymous substitution rates (K_A) in beta-globin genes of related species, suggesting adaptive evolution .

   • Gene Loss in Icefishes: The complete loss of β-globin genes in icefishes contrasts with retained α-globin remnants, underscoring the evolutionary trajectory toward hemoglobinlessness .

Challenges and Future Directions

While recombinant production of N. coriiceps neglecta HBA2 is not explicitly documented, genomic and biochemical data provide a foundation for synthetic biology approaches. Key areas for exploration include:

• Recombinant Expression: Cloning the alpha-globin gene into heterologous systems (e.g., E. coli) to study cold-adapted hemoglobin properties.

• Therapeutic Applications: Investigating whether cold-adapted hemoglobin subunits improve oxygen delivery in hypothermic conditions.