RT Journal Article
SR Electronic
T1 Evolved increases in hemoglobin-oxygen affinity and Bohr effect coincided with the aquatic specialization of penguins
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2020.11.17.387597
DO 10.1101/2020.11.17.387597
A1 Anthony V. Signore
A1 Michael S. Tift
A1 Federico G. Hoffmann
A1 Todd. L. Schmitt
A1 Hideaki Moriyama
A1 Jay F. Storz
YR 2020
UL http://biorxiv.org/content/early/2020/11/18/2020.11.17.387597.abstract
AB Dive capacities of air-breathing vertebrates are dictated by onboard O2 stores, suggesting that physiological specializations of diving birds like penguins may have involved adaptive changes in convective O2 transport. It has been hypothesized that increased hemoglobin (Hb)-O2 affinity improves pulmonary O2 extraction and enhance capacities for breath-hold diving. To investigate evolved changes in Hb function associated with the aquatic specialization of penguins, we integrated comparative measurements of whole-blood and purified native Hbs with protein engineering experiments based on site-directed mutagenesis. We reconstructed and resurrected ancestral Hbs representing the common ancestor of penguins and the more ancient ancestor shared by penguins and their closest nondiving relatives (order Procellariiformes, which includes albatrosses, shearwaters, petrels, and storm petrels). These two ancestors bracket the phylogenetic interval in which penguin-specific changes in Hb function would have evolved. The experiments revealed that penguins evolved a derived increase in Hb-O2 affinity and a greatly augmented Bohr effect (reduced Hb-O2 affinity at low pH). Although an increased Hb-O2 affinity reduces the gradient for O2 diffusion from systemic capillaries to metabolizing cells, this can be compensated by a concomitant enhancement of the Bohr effect, thereby promoting O2 unloading in acidified tissues. We suggest that the evolved increase in Hb-O2 affinity in combination with the augmented Bohr effect maximizes both O2 extraction from the lungs and O2 unloading from the blood, allowing penguins to fully utilize their onboard O2 stores and maximize underwater foraging time.Competing Interest StatementThe authors have declared no competing interest.