Adaptation to extreme environments: structure-function relationships in Emperor penguin haemoglobin

Area of Science:

• Biochemistry
• Physiology
• Evolutionary Biology

Background:

• The Emperor penguin (Aptenodytes forsteri) possesses a unique single hemoglobin (Hb) with functional properties that may be adapted to its extreme environment.
• Understanding these adaptations can provide insights into avian physiology and evolutionary strategies.

Purpose of the Study:

• To investigate the functional properties of Emperor penguin Hb at varying temperatures, proton, and organic phosphate concentrations.
• To establish the complete amino acid sequence and compare it with other hemoglobins, particularly human HbA.
• To correlate functional characteristics with the primary structure of its alpha and beta chains.

Main Methods:

• Functional analysis of Emperor penguin Hb under different conditions (temperature, pH, organic phosphates).
• Amino acid sequencing of the Hb alpha and beta chains.
• Comparative analysis of the primary structure with human HbA and other avian Hbs.

Main Results:

• The amino acid sequence of Emperor penguin Hb was fully determined, revealing 12 substitutions in alpha-beta dimer contact regions compared to human HbA.
• Functional studies indicated an adapted Bohr effect curve suitable for prolonged dives, preventing uncontrolled oxygen release.
• A minor enthalpy change at lower pH suggests adaptation for oxygen delivery insensitive to extreme cold, with a chloride-linked Bohr effect.

Conclusions:

• Emperor penguin Hb displays significant functional adaptations, including a dive-optimized Bohr effect and cold-insensitive oxygen delivery.
• These adaptations are linked to specific structural differences in its primary sequence compared to other avian and human hemoglobins.
• The findings highlight molecular adaptations enabling survival and efficient function in the extreme Antarctic environment.