scholarly journals Evolved increases in hemoglobin-oxygen affinity and the Bohr effect coincided with the aquatic specialization of penguins

2021 ◽  
Vol 118 (13) ◽  
pp. e2023936118
Author(s):  
Anthony V. Signore ◽  
Michael S. Tift ◽  
Federico G. Hoffmann ◽  
Todd. L. Schmitt ◽  
Hideaki Moriyama ◽  
...  
Keyword(s):  
Common Ancestor ◽  
Oxygen Affinity ◽  
Low Ph ◽  
Bohr Effect ◽  
Site Directed Mutagenesis ◽  
Breath Hold ◽  
Directed Mutagenesis ◽  
Hemoglobin Oxygen Affinity ◽  
The Common ◽  
Foraging Time

Dive capacities of air-breathing vertebrates are dictated by onboard O2 stores, suggesting that physiologic specialization of diving birds such as 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 enhances the capacity 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 Hb with protein engineering experiments based on site-directed mutagenesis. We reconstructed and resurrected ancestral Hb 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 (i.e., 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.

scholarly journals Evolved increases in hemoglobin-oxygen affinity and Bohr effect coincided with the aquatic specialization of penguins

2020 ◽  
Author(s):  
Anthony V. Signore ◽  
Michael S. Tift ◽  
Federico G. Hoffmann ◽  
Todd. L. Schmitt ◽  
Hideaki Moriyama ◽  
...  
Keyword(s):  
Common Ancestor ◽  
Oxygen Affinity ◽  
Low Ph ◽  
Bohr Effect ◽  
Site Directed Mutagenesis ◽  
Breath Hold ◽  
Directed Mutagenesis ◽  
Hemoglobin Oxygen Affinity ◽  
The Common ◽  
Foraging Time

AbstractDive 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.

scholarly journals The Bohr/Haldane effect: a model-based uncovering of the full extent of its impact on O2 delivery to and CO2 removal from tissues

2018 ◽  
Vol 125 (3) ◽  
pp. 916-922 ◽  
Author(s):  
Hans Malte ◽  
Gunnar Lykkeboe
Keyword(s):  
Oxygen Affinity ◽  
Model System ◽  
Bohr Effect ◽  
Co2 Removal ◽  
Acid Base ◽  
Oxygen Equilibrium ◽  
Hemoglobin Oxygen Affinity ◽  
Bohr Factor ◽  
O2 Delivery ◽  
Oxygen Equilibrium Curve

For a century, the influence of the Bohr effect on the utilization of blood-borne oxygen has been deemed secondary to its influence on the uptake of carbon dioxide by the blood. Here, we show that the opposite is the case. Using a simple two-ligand, two-state formulation, we modeled the simultaneous oxygen and proton binding to hemoglobin, as well as the resulting acid-base changes of the surrounding solution. Blocking of the Bohr effect in this model system results in a dramatic increase in the oxygen affinity, as expressed by the oxygen partial pressure at half saturation, the P50. It also becomes clear that the P50 and the Bohr factor (a measure of the size of the Bohr effect) are not independent but directly related. Thus, everything else being equal, varying the number of Bohr groups from 0 to 8 per tetramer results in an increase in the Bohr factor from 0 to −0.9 and an increase in P50 from 6 to 46 mmHg at a constant Pco2 of 40 mmHg. Therefore, changes in hemoglobin structure that lead to changes in the Bohr factor will inevitably also change hemoglobin oxygen affinity. NEW & NOTEWORTHY Using a mathematical model, we show that the Bohr effect has a more profound effect on gas exchange than is evident when comparing oxygen equilibrium curves measured in the laboratory at different constant values of Pco2 or pH. Protons preloaded on the Bohr groups, as well as the protons taken up during oxygen unloading, dramatically decrease oxygen affinity of the physiological oxygen equilibrium curve. Therefore, the Bohr effect is instrumental in setting the oxygen affinity.

scholarly journals Recognition of Phosphorylated-Smad2-Containing Complexes by a Novel Smad Interaction Motif

2004 ◽  
Vol 24 (3) ◽  
pp. 1106-1121 ◽  
Author(s):  
Rebecca A. Randall ◽  
Michael Howell ◽  
Christopher S. Page ◽  
Amanda Daly ◽  
Paul A. Bates ◽  
...  
Keyword(s):  
Transcription Factors ◽  
Growth Factor ◽  
Transforming Growth Factor ◽  
Transforming Growth Factor Β ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
Hydrophobic Pocket ◽  
Winged Helix ◽  
The Common ◽  
Necessary And Sufficient

ABSTRACT Transforming growth factor β (TGF-β) superfamily members signal via complexes of activated Smads, comprising phosphorylated receptor-regulated Smads, such as Smad2 and Smad3, and Smad4. These complexes are recruited to DNA by specific transcription factors. The forkhead/winged-helix transcription factors, XFast-1/XFoxH1a and XFast-3/XFoxH1b, bind an activated Smad heterotrimer comprising two Smad2s and one Smad4. Here we identify a novel Smad2 interaction motif, the Fast/FoxH1 motif (FM), present in all known Fast/FoxH1 family members, N-terminal to the common Smad interaction motif (SIM). The FM is necessary and sufficient to bind active Smad2/Smad4 complexes. The FM differs from the SIM since it discriminates between Smad2 and Smad3, and moreover only binds phosphorylated Smad2 in the context of activated Smad complexes. It is the first Smad interaction motif with this property. Site-directed mutagenesis indicates that the binding site for the FM on a Smad2/Smad4 heterotrimer is a hydrophobic pocket that incorporates the Smad/Smad interface. We demonstrate that the presence of an FM and SIM in the Fast/FoxH1 proteins allows them to compete efficiently for activated Smad2/Smad4 complexes with transcription factors such as Mixer that only contain a SIM. This establishes a hierarchy of Smad-interacting transcription factors, determined by their affinity for active Smad complexes.

Studies of haemoglobin functions by site-directed mutagenesis

1986 ◽  
Vol 317 (1540) ◽  
pp. 443-447 ◽  
Keyword(s):  
Expression Vector ◽  
Oxygen Affinity ◽  
Coagulation Factor ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
Oxygen Binding ◽  
Factor X ◽  
Binding Properties ◽  
High Oxygen Affinity ◽  
Alkaline Bohr Effect

Human (3-globin was synthesized in Escherichia coli as a cleavable fusion protein by using the expression vector pLcIIFX|3-globin(nic - ). The authentic (3-globin was liberated by digestion with blood coagulation factor X a and a 2 (3 2 tetramers were reconstituted. The oxygen-binding properties of reconstituted haemoglobin (Hb) were essentially the same as those of human native Hb. Two mutant haemoglobins were constructed by site-directed mutagenesis. HbNymphéas (Cys-93(3->Ser) showed a slightly increased oxygen affinity and diminished co-operativity with normal DPG (2,3-diphosphoglycerate) effect and slightly reduced alkaline Bohr effects. Hb Daphne (Cys-93(3->-Ser, His-143(3->- Arg) showed low co-operativity with high oxygen affinity. The alkaline Bohr effect was slightly reduced, but the DPG effect was enhanced by 50% by the His-143(3^ Arg mutation.

Identification of active-site residues in Bradyrhizobium japonicum malonamidase E2

2000 ◽  
Vol 349 (2) ◽  
pp. 501-507 ◽  
Author(s):  
Hyun Min KOO ◽  
Sung-Ook CHOI ◽  
Hyun Mi KIM ◽  
Yu Sam KIM
Keyword(s):  
Bradyrhizobium Japonicum ◽  
Catalytic Mechanism ◽  
Sequence Similarity ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
Wild Type ◽  
Basic Residue ◽  
High Sequence Similarity ◽  
Signature Sequences ◽  
The Common

Malonamidase (MA) E2 was previously purified and characterized from Bradyrhizobium japonicum USDA 110. The gene encoding this enzyme has been cloned, sequenced and expressed in Escherichia coli. The recombinant MAE2 was purified to homogeneity from the transformed E. coli. The biochemical properties of the recombinant enzyme are essentially identical to those from wild-type B. japonicum. A database search showed that the MAE2 protein has a high sequence similarity with the common signature sequences of the amidase family. The only exception is that the aspartic residue in these signature sequences is replaced by a glutamine residue. In order to identify amino acid residues essential for enzyme activity, a series of site-directed mutagenesis studies and steady-state kinetic experiments were performed. Gln195, Ser199, Cys207 and Lys213 of the common signature sequences were selected for site-directed mutagenesis. Among the mutants, Q195D, Q195E and S199C showed less than 0.02% of the kcat value of the wild-type enzyme, and S199A, Q195L and Q195N exhibited no detectable catalytic activities. Mutants (K213L, K213R and K213H) obtained by replacement of the only conserved basic residue, Lys213, in the signature sequences, also displayed significant reductions (approx. 380-fold) in kcat value, whereas C207A kept full activity. These results suggest that MAE2 may catalyse hydrolysis of malonamate by a novel catalytic mechanism, in which Gln195, Ser199 and Lys213 are involved.

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