Haemoglobin works best at different temperatures in different animals
An international team of scientists, including
ANSTO’s Dr Chris Garvey, have discovered that
haemoglobin molecules have evolved to carry
oxygen best at different body temperatures in
different animals.
Haemoglobin is a protein found in red blood
cells that binds to and carries oxygen.
Haemoglobin binds to oxygen when blood
moves through the lungs, and releases oxygen
as it moves through capillaries in body tissues.
The protein is made up of four polypeptide
chains, and each subunit surrounds a haem
group, where the oxygen can bind.
Scientists already knew that oxygen binding and
release happens most efficiently when the
haemoglobin molecule partly unfolds and
softens.
A representation of a haemoglobin protein, showing
the four haem groups (red), each surrounded by a
polypeptide subunit. These subunits partly unfold to
allow efficient oxygen binding and release. Image
credit: Irving Geis
Environmental factors, such as temperature, can affect the shape and folding of a
protein. Therefore, the team of researchers set out to find out how haemoglobin works
in a range of animals with different body temperatures.
The research team used neutron scattering techniques to measure the flexibility and
softness of haemoglobin at different temperatures. The scientists tested haemoglobin
from three endothermic animals (a human, a platypus, and a chicken) and one
ectothermic animal (a salt-water crocodile).
The scientists found that the haemoglobin protein softened and partly unfolded at the
exact body temperature of each endotherm. However, the folding of the crocodile
haemoglobin did not change much with temperature.
The results suggest that haemoglobin structure has evolved in different endotherms to
work most efficiently at the animal’s body temperature. However, more research is
needed to form strong conclusions about haemoglobin evolution.
References
ANSTO News
http://www.ansto.gov.au/discovering_ansto/media_centre/ansto_connect_stories/stories/neutrons_help_explain_e
volution_of_oxygen_transport_in_the_body
Stadler et al. 2012. Thermal fluctuations of haemoglobin from different species: Adaptation to temperature via
conformational dynamics. Journal of the Royal Society. doi: 10.1098/rsif.2012.0364.