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Pu P, Niu Z, Ma M, Tang X, Chen Q. Convergent High O 2 Affinity but Distinct ATP-Mediated Allosteric Regulation of Hemoglobins in Oviparous and Viviparous Eremias Lizards from the Qinghai-Tibet Plateau. Animals (Basel) 2024; 14:1440. [PMID: 38791658 PMCID: PMC11117339 DOI: 10.3390/ani14101440] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2024] [Revised: 05/04/2024] [Accepted: 05/07/2024] [Indexed: 05/26/2024] Open
Abstract
The functional adaptation and underlying molecular mechanisms of hemoglobins (Hbs) have primarily concentrated on mammals and birds, with few reports on reptiles. This study aimed to investigate the convergent and species-specific high-altitude adaptation mechanisms of Hbs in two Eremias lizards from the Qinghai-Tibet Plateau. The Hbs of high-altitude E. argus and E. multiocellata were characterized by significantly high overall and intrinsic Hb-O2 affinity compared to their low-altitude populations. Despite the similarly low Cl- sensitivities, the Hbs of high-altitude E. argus exhibited higher ATP sensitivity and ATP-dependent Bohr effects than that of E. multiocellata, which could facilitate O2 unloading in respiring tissues. Eremias lizards Hbs exhibited similarly low temperature sensitivities and relatively high Bohr effects at lower temperatures, which could help to stably deliver and release O2 to cold extremities at low temperatures. The oxygenation properties of Hbs in high-altitude populations might be attributed to varying ratios of β2/β1 globin and substitutions on the β2-type globin. Notably, the Asn12Ala in lowland E. argus could cause localized destabilization of the E-helix in the tetrameric Hb by elimination of hydrogen bonds, thereby resulting in its lowest O2 affinity. This study provides a valuable reference for the high-altitude adaptation mechanisms of hemoglobins in reptiles.
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Affiliation(s)
- Peng Pu
- School of Biological and Pharmaceutical Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China;
| | - Zhiyi Niu
- Department of Animal and Biomedical Sciences, School of Life Sciences, Lanzhou University, No. 222 Tianshui South Road, Lanzhou 730000, China; (Z.N.); (M.M.); (X.T.)
| | - Ming Ma
- Department of Animal and Biomedical Sciences, School of Life Sciences, Lanzhou University, No. 222 Tianshui South Road, Lanzhou 730000, China; (Z.N.); (M.M.); (X.T.)
| | - Xiaolong Tang
- Department of Animal and Biomedical Sciences, School of Life Sciences, Lanzhou University, No. 222 Tianshui South Road, Lanzhou 730000, China; (Z.N.); (M.M.); (X.T.)
| | - Qiang Chen
- Department of Animal and Biomedical Sciences, School of Life Sciences, Lanzhou University, No. 222 Tianshui South Road, Lanzhou 730000, China; (Z.N.); (M.M.); (X.T.)
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2
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Storz JF, Bautista NM. Altitude acclimatization, hemoglobin-oxygen affinity, and circulatory oxygen transport in hypoxia. Mol Aspects Med 2022; 84:101052. [PMID: 34879970 PMCID: PMC8821351 DOI: 10.1016/j.mam.2021.101052] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Revised: 11/12/2021] [Accepted: 11/15/2021] [Indexed: 01/01/2023]
Abstract
In mammals and other air-breathing vertebrates that live at high altitude, adjustments in convective O2 transport via changes in blood hemoglobin (Hb) content and/or Hb-O2 affinity can potentially mitigate the effects of arterial hypoxemia. However, there are conflicting views about the optimal values of such traits in hypoxia, partly due to the intriguing observation that hypoxia-induced acclimatization responses in humans and other predominantly lowland mammals are frequently not aligned in the same direction as evolved phenotypic changes in high-altitude natives. Here we review relevant theoretical and empirical results and we highlight experimental studies of rodents and humans that provide insights into the combination of hematological changes that help attenuate the decline in aerobic performance in hypoxia. For a given severity of hypoxia, experimental results suggest that optimal values for hematological traits are conditional on the states of other interrelated phenotypes that govern different steps in the O2-transport pathway.
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Affiliation(s)
- Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, NE, USA.
| | - Naim M Bautista
- School of Biological Sciences, University of Nebraska, Lincoln, NE, USA
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3
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Ivy CM, Wearing OH, Natarajan C, Schweizer RM, Gutiérrez-Pinto N, Velotta JP, Campbell-Staton SC, Petersen EE, Fago A, Cheviron ZA, Storz JF, Scott GR. Genetic variation in haemoglobin is associated with evolved changes in breathing in high-altitude deer mice. J Exp Biol 2022; 225:273749. [PMID: 34913467 PMCID: PMC8917448 DOI: 10.1242/jeb.243595] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2021] [Accepted: 12/09/2021] [Indexed: 01/21/2023]
Abstract
Physiological systems often have emergent properties but the effects of genetic variation on physiology are often unknown, which presents a major challenge to understanding the mechanisms of phenotypic evolution. We investigated whether genetic variants in haemoglobin (Hb) that contribute to high-altitude adaptation in deer mice (Peromyscus maniculatus) are associated with evolved changes in the control of breathing. We created F2 inter-population hybrids of highland and lowland deer mice to test for phenotypic associations of α- and β-globin variants on a mixed genetic background. Hb genotype had expected effects on Hb-O2 affinity that were associated with differences in arterial O2 saturation in hypoxia. However, high-altitude genotypes were also associated with breathing phenotypes that should contribute to enhancing O2 uptake in hypoxia. Mice with highland α-globin exhibited a more effective breathing pattern, with highland homozygotes breathing deeper but less frequently across a range of inspired O2, and this difference was comparable to the evolved changes in breathing pattern in deer mouse populations native to high altitude. The ventilatory response to hypoxia was augmented in mice that were homozygous for highland β-globin. The association of globin variants with variation in breathing phenotypes could not be recapitulated by acute manipulation of Hb-O2 affinity, because treatment with efaproxiral (a synthetic drug that acutely reduces Hb-O2 affinity) had no effect on breathing in normoxia or hypoxia. Therefore, adaptive variation in Hb may have unexpected effects on physiology in addition to the canonical function of this protein in circulatory O2 transport.
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Affiliation(s)
- Catherine M. Ivy
- Department of Biology, McMaster University, Hamilton, ON, Canada, L8S 4K1,Author for correspondence ()
| | - Oliver H. Wearing
- Department of Biology, McMaster University, Hamilton, ON, Canada, L8S 4K1
| | | | - Rena M. Schweizer
- Divison of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | | | - Jonathan P. Velotta
- Divison of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Shane C. Campbell-Staton
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA 90095, USA
| | - Elin E. Petersen
- Department of Biology, Aarhus University, 8000 Aarhus C, Denmark
| | - Angela Fago
- Department of Biology, Aarhus University, 8000 Aarhus C, Denmark
| | - Zachary A. Cheviron
- Divison of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Jay F. Storz
- School of Biological Sciences, University of Nebraska, Lincoln, NE 68588, USA
| | - Graham R. Scott
- Department of Biology, McMaster University, Hamilton, ON, Canada, L8S 4K1
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Pu P, Zhao Y, Niu Z, Cao W, Zhang T, He J, Wang J, Tang X, Chen Q. Comparison of hematological traits and oxygenation properties of hemoglobins from highland and lowland Asiatic toad (Bufo gargarizans). J Comp Physiol B 2021; 191:1019-1029. [PMID: 33876256 DOI: 10.1007/s00360-021-01368-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Revised: 03/13/2021] [Accepted: 04/07/2021] [Indexed: 01/09/2023]
Abstract
The Asiatic toad (Bufo gargarizans) belonging to the family of Bufonidae (Anura: Amphibia) is successfully residing on the Qinghai-Tibetan Plateau (QTP). To investigate whether the oxygen delivery undergoes adaptive adjustments to high-altitude environments in Asian toads inhabiting the QTP (Zoige County, 3446 m), choosing low-altitude populations (Chengdu City, 500 m) as control, we measured hematological traits, O2 affinities of whole blood, Hb-O2 affinities of purified Hbs, their sensitivities to temperature, and allosteric effectors (H+, Cl- and ATP). Our results showed that high-altitude Asiatic toads possessed significantly increased hemoglobin concentration, hematocrit, and red blood cell count, but significantly decreased erythrocyte volume compared with low-altitude toads. The whole blood and purified Hbs of high-altitude Asiatic toads both exhibited significantly higher O2 affinities compared with low-altitude toads. Substantially increased intrinsic Hb-O2 affinities of high-altitude Asiatic toads Hbs are likely to be the main reason for its elevated Hb-O2 affinities given the anionic cofactor sensitivities of high- and low-altitude toads were similar. The Hbs of high-altitude toads were also characterized by distinctly strong Bohr effects at the low temperature and low-temperature sensitivities. The adaptive adjustments of hematological traits could enhance the blood-O2 carrying capacity of high-altitude Asiatic toads. The increased Hb-O2 affinities could safeguard the pulmonary O2 uploading under hypoxia. The strong Bohr effects at the low temperature could help the release of O2 in metabolic tissues and cold limbs, while low-temperature sensitivity could minimize the effect of temperature fluctuation on the Hb-O2 affinity.
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Affiliation(s)
- Peng Pu
- Department of Animal and Biomedical Sciences, School of Life Science, Lanzhou University, Lanzhou, 730000, Gansu, China
| | - Yao Zhao
- Department of Animal and Biomedical Sciences, School of Life Science, Lanzhou University, Lanzhou, 730000, Gansu, China
| | - Zhiyi Niu
- Department of Animal and Biomedical Sciences, School of Life Science, Lanzhou University, Lanzhou, 730000, Gansu, China
| | - Wangjie Cao
- Department of Animal and Biomedical Sciences, School of Life Science, Lanzhou University, Lanzhou, 730000, Gansu, China
| | - Tao Zhang
- Department of Animal and Biomedical Sciences, School of Life Science, Lanzhou University, Lanzhou, 730000, Gansu, China
| | - Jie He
- Department of Animal and Biomedical Sciences, School of Life Science, Lanzhou University, Lanzhou, 730000, Gansu, China
| | - Jinzhou Wang
- Department of Animal and Biomedical Sciences, School of Life Science, Lanzhou University, Lanzhou, 730000, Gansu, China
| | - Xiaolong Tang
- Department of Animal and Biomedical Sciences, School of Life Science, Lanzhou University, Lanzhou, 730000, Gansu, China
| | - Qiang Chen
- Department of Animal and Biomedical Sciences, School of Life Science, Lanzhou University, Lanzhou, 730000, Gansu, China.
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5
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Correlation between convection requirement and carotid body responses to hypoxia and hemoglobin affinity: comparison between two rat strains. J Comp Physiol B 2021; 191:1031-1045. [PMID: 33970341 DOI: 10.1007/s00360-021-01377-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 03/31/2021] [Accepted: 04/13/2021] [Indexed: 02/06/2023]
Abstract
We tested the hypothesis that differences in ventilatory ([Formula: see text]) or convection requirement ([Formula: see text]/[Formula: see text]O2) response to hypoxia would be correlated with differences in hemoglobin (Hb) oxygen affinity between two strains of rats, as they have been shown to be among several species of mammals, birds and reptiles. Brown Norway (BN) rats reduce metabolism more than they increase ventilation in response to hypoxia and both the ventilatory and convection requirement responses to hypoxia are lower in the BN than the Sprague-Dawley (SD) rat. The lower threshold of the ventilation/convection requirement responses of the BN to hypoxia are associated with a higher affinity Hb than the SD rats, (P50 values of 32.4 (± 0.6) versus 34.4 (± 0.5), respectively (P < 0.05), and P75 values of 46.1 (± 0.5) for BN versus 50.7 (± 0.8) for SD (P < 0.001). This significant difference, particularly near the inflection point of the dissociation curve, supported our hypothesis. A reduced sensitivity of BN compared to SD carotid bodies was found. BN carotid bodies (from 36 20-60-day-olds) had a mean estimated volume of 26.64 ± 1.47 × 106 μm3, significantly (P < 0.0001) smaller than SD carotid bodies (from 46 16-40-day-olds) at 50.66 ± 3.41 × 106 μm3. Both genetic and epigenetic/developmental mechanisms may account for the observed inter-strain differences.
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Scott GR, Dalziel AC. Physiological insight into the evolution of complex phenotypes: aerobic performance and the O2 transport pathway of vertebrates. J Exp Biol 2021; 224:271829. [PMID: 34387318 DOI: 10.1242/jeb.210849] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Evolutionary physiology strives to understand how the function and integration of physiological systems influence the way in which organisms evolve. Studies of the O2 transport pathway - the integrated physiological system that transports O2 from the environment to mitochondria - are well suited to this endeavour. We consider the mechanistic underpinnings across the O2 pathway for the evolution of aerobic capacity, focusing on studies of artificial selection and naturally selected divergence among wild populations of mammals and fish. We show that evolved changes in aerobic capacity do not require concerted changes across the O2 pathway and can arise quickly from changes in one or a subset of pathway steps. Population divergence in aerobic capacity can be associated with the evolution of plasticity in response to environmental variation or activity. In some cases, initial evolutionary divergence of aerobic capacity arose exclusively from increased capacities for O2 diffusion and/or utilization in active O2-consuming tissues (muscle), which may often constitute first steps in adaptation. However, continued selection leading to greater divergence in aerobic capacity is often associated with increased capacities for circulatory and pulmonary O2 transport. Increases in tissue O2 diffusing capacity may augment the adaptive benefit of increasing circulatory O2 transport owing to their interactive influence on tissue O2 extraction. Theoretical modelling of the O2 pathway suggests that O2 pathway steps with a disproportionately large influence over aerobic capacity have been more likely to evolve, but more work is needed to appreciate the extent to which such physiological principles can predict evolutionary outcomes.
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Affiliation(s)
- Graham R Scott
- Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4K1, Canada
| | - Anne C Dalziel
- Department of Biology, Saint Mary's University, 923 Robie Street, Halifax, Nova Scotia, B3H 3C3, Canada
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7
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The adaptive benefit of evolved increases in hemoglobin-O 2 affinity is contingent on tissue O 2 diffusing capacity in high-altitude deer mice. BMC Biol 2021; 19:128. [PMID: 34158035 PMCID: PMC8218429 DOI: 10.1186/s12915-021-01059-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2020] [Accepted: 05/28/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Complex organismal traits are often the result of multiple interacting genes and sub-organismal phenotypes, but how these interactions shape the evolutionary trajectories of adaptive traits is poorly understood. We examined how functional interactions between cardiorespiratory traits contribute to adaptive increases in the capacity for aerobic thermogenesis (maximal O2 consumption, V̇O2max, during acute cold exposure) in high-altitude deer mice (Peromyscus maniculatus). We crossed highland and lowland deer mice to produce F2 inter-population hybrids, which expressed genetically based variation in hemoglobin (Hb) O2 affinity on a mixed genetic background. We then combined physiological experiments and mathematical modeling of the O2 transport pathway to examine the links between cardiorespiratory traits and V̇O2max. RESULTS Physiological experiments revealed that increases in Hb-O2 affinity of red blood cells improved blood oxygenation in hypoxia but were not associated with an enhancement in V̇O2max. Sensitivity analyses performed using mathematical modeling showed that the influence of Hb-O2 affinity on V̇O2max in hypoxia was contingent on the capacity for O2 diffusion in active tissues. CONCLUSIONS These results suggest that increases in Hb-O2 affinity would only have adaptive value in hypoxic conditions if concurrent with or preceded by increases in tissue O2 diffusing capacity. In high-altitude deer mice, the adaptive benefit of increasing Hb-O2 affinity is contingent on the capacity to extract O2 from the blood, which helps resolve controversies about the general role of hemoglobin function in hypoxia tolerance.
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8
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Wearing OH, Scott GR. Commentary: Hierarchical reductionism approach to understanding adaptive variation in animal performance. Comp Biochem Physiol B Biochem Mol Biol 2021; 256:110636. [PMID: 34119652 DOI: 10.1016/j.cbpb.2021.110636] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2021] [Revised: 06/04/2021] [Accepted: 06/07/2021] [Indexed: 12/20/2022]
Abstract
Aerobic capacity is a complex performance trait with important consequences for fitness, and is determined by the integrated function of the O2 transport pathway. The components of the O2 pathway interact and function as an integrated physiological system, which could strongly influence the contribution of each component to variation in aerobic capacity. In this commentary, we highlight the value of hierarchical reductionism - combining studies of how component parts work in isolation with studies of how components interact within integrated systems - for understanding the evolution of aerobic capacity. This is achieved by focussing on the role of haemoglobin in adaptive increases in aerobic capacity in high-altitude deer mice (Peromyscus maniculatus). High-altitude deer mice have evolved increased aerobic capacity in hypoxia, in association with evolved changes in several subordinate traits across the O2 pathway. This includes an evolved increase in Hb-O2 affinity - which helps safeguard arterial O2 saturation in hypoxia - and reductionist approaches have been successful at identifying the genetic, structural, and biochemical underpinnings of variation in this trait. However, theoretical modelling and empirical measurements suggest that increased Hb-O2 affinity may not augment aerobic capacity on its own. The adaptive benefit of increased Hb-O2 affinity in high-altitude deer mice appears to have been contingent upon antecedent changes in other traits in the O2 pathway, particularly an increased capacity for O2 diffusion and utilization in active tissues. These findings highlight the importance of understanding the interactions between the components of integrated systems for fully appreciating the evolution of complex performance phenotypes.
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Affiliation(s)
- Oliver H Wearing
- Department of Biology, McMaster University, Hamilton, ON L8S 4K1, Canada.
| | - Graham R Scott
- Department of Biology, McMaster University, Hamilton, ON L8S 4K1, Canada
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9
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Storz JF. High-Altitude Adaptation: Mechanistic Insights from Integrated Genomics and Physiology. Mol Biol Evol 2021; 38:2677-2691. [PMID: 33751123 PMCID: PMC8233491 DOI: 10.1093/molbev/msab064] [Citation(s) in RCA: 56] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Population genomic analyses of high-altitude humans and other vertebrates have identified numerous candidate genes for hypoxia adaptation, and the physiological pathways implicated by such analyses suggest testable hypotheses about underlying mechanisms. Studies of highland natives that integrate genomic data with experimental measures of physiological performance capacities and subordinate traits are revealing associations between genotypes (e.g., hypoxia-inducible factor gene variants) and hypoxia-responsive phenotypes. The subsequent search for causal mechanisms is complicated by the fact that observed genotypic associations with hypoxia-induced phenotypes may reflect second-order consequences of selection-mediated changes in other (unmeasured) traits that are coupled with the focal trait via feedback regulation. Manipulative experiments to decipher circuits of feedback control and patterns of phenotypic integration can help identify causal relationships that underlie observed genotype–phenotype associations. Such experiments are critical for correct inferences about phenotypic targets of selection and mechanisms of adaptation.
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Affiliation(s)
- Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, NE, USA
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10
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Abstract
Population genomic studies of humans and other animals at high altitude have generated many hypotheses about the genes and pathways that may have contributed to hypoxia adaptation. Future advances require experimental tests of such hypotheses to identify causal mechanisms. Studies to date illustrate the challenge of moving from lists of candidate genes to the identification of phenotypic targets of selection, as it can be difficult to determine whether observed genotype-phenotype associations reflect causal effects or secondary consequences of changes in other traits that are linked via homeostatic regulation. Recent work on high-altitude models such as deer mice has revealed both plastic and evolved changes in respiratory, cardiovascular, and metabolic traits that contribute to aerobic performance capacity in hypoxia, and analyses of tissue-specific transcriptomes have identified changes in regulatory networks that mediate adaptive changes in physiological phenotype. Here we synthesize recent results and discuss lessons learned from studies of high-altitude adaptation that lie at the intersection of genomics and physiology.
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Affiliation(s)
- Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, Nebraska 68588, USA;
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, Montana 59812, USA;
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11
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Bellelli A, Brunori M. Control of Oxygen Affinity in Mammalian Hemoglobins: Implications for a System Biology Description of the Respiratory Properties of the Red Blood Cell. Curr Protein Pept Sci 2021; 21:553-572. [PMID: 32013829 DOI: 10.2174/1389203721666200203151414] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Revised: 01/22/2020] [Accepted: 01/23/2020] [Indexed: 11/22/2022]
Abstract
Hemoglobin and myoglobin have been considered for a long time the paradigmatic model systems for protein function, to the point of being defined the "hydrogen atom[s] of biology". Given this privileged position and the huge amount of quantitative information available on these proteins, the red blood cell might appear as the model system and"hydrogen atom" of system biology. Indeed, since the red cell's main function is O2 transport by hemoglobin, the gap between the protein and the cell may appear quite small. Yet, a surprisingly large amount of detailed biochemical information is required for the modelization of the respiratory properties of the erythrocyte. This problem is compounded if modelization aims at uncovering or explaining evolutionarily selected functional properties of hemoglobin. The foremost difficulty lies in the fact that hemoglobins having different intrinsic properties and relatively ancient evolutionary divergence may behave similarly in the complex milieu of blood, whereas very similar hemoglobins sharing a substantial sequence similarity may present important functional differences because of the mutation of a few key residues. Thus, the functional properties of hemoglobin and blood may reflect more closely the recent environmental challenges than the remote evolutionary history of the animal. We summarize in this review the case of hemoglobins from mammals, in an attempt to provide a reasoned summary of their complexity that, we hope, may be of help to scientists interested in the quantitative exploration of the evolutionary physiology of respiration. Indeed the basis of a meaningful modelization of the red cell requires a large amount of information collected in painstaking and often forgotten studies of the biochemical properties of hemoglobin carried out over more than a century.
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Affiliation(s)
- Andrea Bellelli
- Department of Biochemical Sciences "A. Rossi Fanelli", Sapienza University of Rome, Rome, Italy
| | - Maurizio Brunori
- Accademia Nazionale dei Lincei, Palazzo Corsini, Via della Lungara, Roma, Italy
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12
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Pu P, Lu S, Niu Z, Zhang T, Zhao Y, Yang X, Zhao Y, Tang X, Chen Q. Oxygenation properties and underlying molecular mechanisms of hemoglobins in plateau zokor ( Eospalax baileyi). Am J Physiol Regul Integr Comp Physiol 2019; 317:R696-R708. [PMID: 31508994 DOI: 10.1152/ajpregu.00335.2018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The plateau zokor (Eospalax baileyi) is a species of subterranean rodent endemic to the Tibetan Plateau. It is well adapted to the cold and hypoxic and hypercapnic burrow. To study the oxygenation properties of plateau zokor hemoglobins (Hbs), we measured intrinsic Hb-O2 affinities and their sensitivities to pH (Bohr effect); CO2; Cl-, 2,3-diphosphoglycerate (DPG); and temperature using purified Hbs from zokor and mouse. The optimal deoxyHb model of plateau zokor was constructed and used to study its structural characteristics by molecular dynamics simulations. O2 binding results revealed that plateau zokor Hbs exhibit remarkably high intrinsic Hb-O2 affinity, low CO2 effects compared with human and the relatively low anion allosteric effector sensitivities (DPG and Cl-) at normal temperature, which would safeguard the pulmonary Hb-O2 loading under hypoxic and hypercapnic conditions. Furthermore, the high anion allosteric effector sensitivities at low temperature and low temperature sensitivities of plateau zokor Hbs would facilitate the releasing of O2 in cold extremities and metabolic tissues. However, the high Hb-O2 affinity of plateau zokor is not compensated by high pH sensitivity as the Bohr factors of plateau zokor Hbs were as low as those of mouse. The results of molecular dynamics simulations revealed the reduced hydrogen bonding between the α1β1- and α2β2-dimer interface of deoxyHb in zokor compared with mouse. It may be the primary mechanism of the high intrinsic Hb-O2 affinities in zokor. Specifically, substitution of the 131Ser→Asn in the α2-chain weakened the connection between α1- and β2-subunit.
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Affiliation(s)
- Peng Pu
- Institute of Biochemistry and Molecular Biology, School of Life Science, Lanzhou University, Lanzhou, Gansu, China
| | - Songsong Lu
- Faculty of Forestry, Gansu Agricultural University, Lanzhou, Gansu, China
| | - Zhiyi Niu
- Institute of Biochemistry and Molecular Biology, School of Life Science, Lanzhou University, Lanzhou, Gansu, China
| | - Tao Zhang
- Institute of Biochemistry and Molecular Biology, School of Life Science, Lanzhou University, Lanzhou, Gansu, China
| | - Yaofeng Zhao
- Institute of Biochemistry and Molecular Biology, School of Life Science, Lanzhou University, Lanzhou, Gansu, China
| | - Xingwen Yang
- Institute of Biochemistry and Molecular Biology, School of Life Science, Lanzhou University, Lanzhou, Gansu, China
| | - Yao Zhao
- Institute of Biochemistry and Molecular Biology, School of Life Science, Lanzhou University, Lanzhou, Gansu, China
| | - Xiaolong Tang
- Institute of Biochemistry and Molecular Biology, School of Life Science, Lanzhou University, Lanzhou, Gansu, China
| | - Qiang Chen
- Institute of Biochemistry and Molecular Biology, School of Life Science, Lanzhou University, Lanzhou, Gansu, China
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13
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Storz JF, Scott GR. Life Ascending: Mechanism and Process in Physiological Adaptation to High-Altitude Hypoxia. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2019; 50:503-526. [PMID: 33033467 DOI: 10.1146/annurev-ecolsys-110218-025014] [Citation(s) in RCA: 64] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
To cope with the reduced availability of O2 at high altitude, air-breathing vertebrates have evolved myriad adjustments in the cardiorespiratory system to match tissue O2 delivery with metabolic O2 demand. We explain how changes at interacting steps of the O2 transport pathway contribute to plastic and evolved changes in whole-animal aerobic performance under hypoxia. In vertebrates native to high altitude, enhancements of aerobic performance under hypoxia are attributable to a combination of environmentally induced and evolved changes in multiple steps of the pathway. Additionally, evidence suggests that many high-altitude natives have evolved mechanisms for attenuating maladaptive acclimatization responses to hypoxia, resulting in counter-gradient patterns of altitudinal variation for key physiological phenotypes. For traits that exhibit counteracting environmental and genetic effects, evolved changes in phenotype may be cryptic under field conditions and can only be revealed by rearing representatives of high-and low-altitude populations under standardized environmental conditions to control for plasticity.
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Affiliation(s)
- Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, Nebraska 68588, USA
| | - Graham R Scott
- Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada
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14
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Storz JF, Cheviron ZA, McClelland GB, Scott GR. Evolution of physiological performance capacities and environmental adaptation: insights from high-elevation deer mice ( Peromyscus maniculatus). J Mammal 2019; 100:910-922. [PMID: 31138949 DOI: 10.1093/jmammal/gyy173] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Accepted: 12/14/2018] [Indexed: 12/14/2022] Open
Abstract
Analysis of variation in whole-animal performance can shed light on causal connections between specific traits, integrated physiological capacities, and Darwinian fitness. Here, we review and synthesize information on naturally occurring variation in physiological performance capacities and how it relates to environmental adaptation in deer mice (Peromyscus maniculatus). We discuss how evolved changes in aerobic exercise capacity and thermogenic capacity have contributed to adaptation to high elevations. Comparative work on deer mice at high and low elevations has revealed evolved differences in aerobic performance capacities in hypoxia. Highland deer mice have consistently higher aerobic performance capacities under hypoxia relative to lowland natives, consistent with the idea that it is beneficial to have a higher maximal metabolic rate (as measured by the maximal rate of O2 consumption, VO2max) in an environment characterized by lower air temperatures and lower O2 availability. Observed differences in aerobic performance capacities between highland and lowland deer mice stem from changes in numerous subordinate traits that alter the flux capacity of the O2-transport system, the oxidative capacity of tissue mitochondria, and the relationship between O2 consumption and ATP synthesis. Many such changes in physiological phenotype are associated with hypoxia-induced changes in gene expression. Research on natural variation in whole-animal performance forms a nexus between physiological ecology and evolutionary biology that requires insight into the natural history of the study species.
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Affiliation(s)
- Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, NE, USA
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
| | | | - Graham R Scott
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
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15
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Dane DM, Cao K, Lu H, Yilmaz C, Dolan J, Thaler CD, Ravikumar P, Hammond KA, Hsia CCW. Acclimatization of low altitude-bred deer mice ( Peromyscus maniculatus) to high altitude. J Appl Physiol (1985) 2018; 125:1411-1423. [PMID: 30091664 DOI: 10.1152/japplphysiol.01036.2017] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
A colony of deer mice subspecies ( Peromyscus maniculatus sonoriensis) native to high altitude (HA) has been maintained at sea level for 18-20 generations and remains genetically unchanged. To determine if these animals retain responsiveness to hypoxia, one group (9-11 wk old) was acclimated to HA (3,800 m) for 8 wk. Age-matched control animals were acclimated to a lower altitude (LA; 252 m). Maximal O2 uptake (V̇o2max) was measured at the respective altitudes. On a separate day, lung volume, diffusing capacity for carbon monoxide (DLCO), and pulmonary blood flow were measured under anesthesia using a rebreathing technique at two inspired O2 tensions. The HA-acclimated deer mice maintained a normal V̇o2max relative to LA baseline. Compared with LA control mice, antemortem lung volume was larger in HA mice in a manner dependent on alveolar O2 tension. Systemic hematocrit, pulmonary blood flow, and standardized DLCO did not differ significantly between groups. HA mice showed a higher postmortem alveolar-capillary hematocrit, larger alveolar ducts, and smaller distal conducting structures. In HA mice, absolute volumes of alveolar type I epithelia and endothelia were higher whereas that of interstitia was lower than in LA mice. These structural changes occurred without a net increase in whole-lung septal tissue-capillary volumes or surface areas. Thus, deer mice bred and raised to adulthood at LA retain phenotypic plasticity and adapt to HA without a decrement in V̇o2max via structural (enlarged airspaces, alveolar septal remodeling) and nonstructural (lung expansion under hypoxia) mechanisms and without an increase in systemic hematocrit or compensatory lung growth. NEW & NOTEWORTHY Deer mice ( Peromyscus maniculatus) are robust and very active mammals that are found across the North American continent. They are also highly adaptable to extreme environments. When introduced to high altitude they retain remarkable adaptive ability to the low-oxygen environment via lung expansion and remodeling of existing lung structure, thereby maintaining normal aerobic capacity without generating more red blood cells or additional lung tissue.
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Affiliation(s)
- D Merrill Dane
- Department of Internal Medicine, University of Texas Southwestern Medical Center , Dallas, Texas
| | - Khoa Cao
- Department of Internal Medicine, University of Texas Southwestern Medical Center , Dallas, Texas
| | - Hua Lu
- Department of Internal Medicine, University of Texas Southwestern Medical Center , Dallas, Texas
| | - Cuneyt Yilmaz
- Department of Internal Medicine, University of Texas Southwestern Medical Center , Dallas, Texas
| | - Jamie Dolan
- Department of Evolution, Ecology and Organismal Biology, University of California at Riverside , Riverside, California
| | - Catherine D Thaler
- Department of Evolution, Ecology and Organismal Biology, University of California at Riverside , Riverside, California
| | - Priya Ravikumar
- Department of Internal Medicine, University of Texas Southwestern Medical Center , Dallas, Texas
| | - Kimberly A Hammond
- Department of Evolution, Ecology and Organismal Biology, University of California at Riverside , Riverside, California
| | - Connie C W Hsia
- Department of Internal Medicine, University of Texas Southwestern Medical Center , Dallas, Texas
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Russo R, Giordano D, Paredi G, Marchesani F, Milazzo L, Altomonte G, Del Canale P, Abbruzzetti S, Ascenzi P, di Prisco G, Viappiani C, Fago A, Bruno S, Smulevich G, Verde C. The Greenland shark Somniosus microcephalus-Hemoglobins and ligand-binding properties. PLoS One 2017; 12:e0186181. [PMID: 29023598 PMCID: PMC5638460 DOI: 10.1371/journal.pone.0186181] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Accepted: 09/26/2017] [Indexed: 11/18/2022] Open
Abstract
A large amount of data is currently available on the adaptive mechanisms of polar bony fish hemoglobins, but structural information on those of cartilaginous species is scarce. This study presents the first characterisation of the hemoglobin system of one of the longest-living vertebrate species (392 ± 120 years), the Arctic shark Somniosus microcephalus. Three major hemoglobins are found in its red blood cells and are made of two copies of the same α globin combined with two copies of three very similar β subunits. The three hemoglobins show very similar oxygenation and carbonylation properties, which are unaffected by urea, a very important compound in marine elasmobranch physiology. They display identical electronic absorption and resonance Raman spectra, indicating that their heme-pocket structures are identical or highly similar. The quaternary transition equilibrium between the relaxed (R) and the tense (T) states is more dependent on physiological allosteric effectors than in human hemoglobin, as also demonstrated in polar teleost hemoglobins. Similar to other cartilaginous fishes, we found no evidence for functional differentiation among the three isoforms. The very similar ligand-binding properties suggest that regulatory control of O2 transport may be at the cellular level and that it may involve changes in the cellular concentrations of allosteric effectors and/or variations of other systemic factors. The hemoglobins of this polar shark have evolved adaptive decreases in O2 affinity in comparison to temperate sharks.
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Affiliation(s)
- Roberta Russo
- Institute of Biosciences and BioResources, CNR, Via Pietro Castellino 111, Naples, Italy
| | - Daniela Giordano
- Institute of Biosciences and BioResources, CNR, Via Pietro Castellino 111, Naples, Italy
- Stazione Zoologica Anton Dohrn, Villa Comunale, Naples, Italy
| | - Gianluca Paredi
- Dipartimento di Scienze degli Alimenti e del Farmaco, Università di Parma, Parco Area delle Scienze 23/A, Parma, Italy
| | - Francesco Marchesani
- Dipartimento di Scienze degli Alimenti e del Farmaco, Università di Parma, Parco Area delle Scienze 23/A, Parma, Italy
| | - Lisa Milazzo
- Dipartimento di Chimica “Ugo Schiff”, Università di Firenze, Via della Lastruccia 3–13, Sesto Fiorentino (FI), Italy
| | - Giovanna Altomonte
- Institute of Biosciences and BioResources, CNR, Via Pietro Castellino 111, Naples, Italy
- Dipartimento di Biologia, Università Roma 3, Viale Marconi 448, Roma, Italy
| | - Pietro Del Canale
- Dipartimento di Scienze Matematiche, Fisiche e Informatiche, Università degli Studi di Parma, Parco Area delle Scienze 7A, Parma, Italy
| | - Stefania Abbruzzetti
- Dipartimento di Scienze Matematiche, Fisiche e Informatiche, Università degli Studi di Parma, Parco Area delle Scienze 7A, Parma, Italy
- NEST Istituto Nanoscienze, CNR, Piazza San Silvestro 12, Pisa, Italy
| | - Paolo Ascenzi
- Laboratorio Interdipartimentale di Microscopia Elettronica, Università RomaTre, Via della Vasca Navale 79, Roma, Italy
| | - Guido di Prisco
- Institute of Biosciences and BioResources, CNR, Via Pietro Castellino 111, Naples, Italy
| | - Cristiano Viappiani
- Dipartimento di Scienze Matematiche, Fisiche e Informatiche, Università degli Studi di Parma, Parco Area delle Scienze 7A, Parma, Italy
- NEST Istituto Nanoscienze, CNR, Piazza San Silvestro 12, Pisa, Italy
| | - Angela Fago
- Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark
| | - Stefano Bruno
- Dipartimento di Scienze degli Alimenti e del Farmaco, Università di Parma, Parco Area delle Scienze 23/A, Parma, Italy
| | - Giulietta Smulevich
- Dipartimento di Chimica “Ugo Schiff”, Università di Firenze, Via della Lastruccia 3–13, Sesto Fiorentino (FI), Italy
| | - Cinzia Verde
- Institute of Biosciences and BioResources, CNR, Via Pietro Castellino 111, Naples, Italy
- Stazione Zoologica Anton Dohrn, Villa Comunale, Naples, Italy
- Dipartimento di Biologia, Università Roma 3, Viale Marconi 448, Roma, Italy
- * E-mail: ,
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Petersen AG, Petersen SV, Frische S, Drakulic S, Golas MM, Sander B, Fago A. Hemoglobin polymerization via disulfide bond formation in the hypoxia-tolerant turtle Trachemys scripta: implications for antioxidant defense and O 2 transport. Am J Physiol Regul Integr Comp Physiol 2017; 314:R84-R93. [PMID: 28877869 DOI: 10.1152/ajpregu.00024.2017] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The ability of many reptilian hemoglobins (Hbs) to form high-molecular weight polymers, albeit known for decades, has not been investigated in detail. Given that turtle Hbs often contain a high number of cysteine (Cys), potentially contributing to the red blood cell defense against reactive oxygen species, we have examined whether polymerization of Hb could occur via intermolecular disulfide bonds in red blood cells of freshwater turtle Trachemys scripta, a species that is highly tolerant of hypoxia and oxidative stress. We find that one of the two Hb isoforms of the hemolysate HbA is prone to polymerization in vitro into linear flexible chains of different size that are visible by electron microscopy but not the HbD isoform. Polymerization of purified HbA is favored by hydrogen peroxide, a main cellular reactive oxygen species and a thiol oxidant, and inhibited by thiol reduction and alkylation, indicating that HbA polymerization is due to disulfide bonds. By using mass spectrometry, we identify Cys5 of the αA-subunit of HbA as specifically responsible for forming disulfide bonds between adjacent HbA tetramers. Polymerization of HbA does not affect oxygen affinity, cooperativity, and sensitivity to the allosteric cofactor ATP, indicating that HbA is still fully functional. Polymers also form in T. scripta blood after exposure to anoxia but not normoxia, indicating that they are of physiological relevance. Taken together, these results show that HbA polymers may form during oxidative stress and that Cys5αA of HbA is a key element of the antioxidant capacity of turtle red blood cells.
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Affiliation(s)
| | | | | | - Srdja Drakulic
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Monika M Golas
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
| | - Bjoern Sander
- Centre for Stochastic Geometry and Advanced Bioimaging, Aarhus University , Aarhus , Denmark
| | - Angela Fago
- Department of Bioscience, Aarhus University , Aarhus , Denmark
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18
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Inoguchi N, Mizuno N, Baba S, Kumasaka T, Natarajan C, Storz JF, Moriyama H. Alteration of the α1β2/α2β1 subunit interface contributes to the increased hemoglobin-oxygen affinity of high-altitude deer mice. PLoS One 2017; 12:e0174921. [PMID: 28362841 PMCID: PMC5376325 DOI: 10.1371/journal.pone.0174921] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2017] [Accepted: 03/17/2017] [Indexed: 11/23/2022] Open
Abstract
BACKGROUND Deer mice (Peromyscus maniculatus) that are native to high altitudes in the Rocky Mountains have evolved hemoglobins with an increased oxygen-binding affinity relative to those of lowland conspecifics. To elucidate the molecular mechanisms responsible for the evolved increase in hemoglobin-oxygen affinity, the crystal structure of the highland hemoglobin variant was solved and compared with the previously reported structure for the lowland variant. RESULTS Highland hemoglobin yielded at least two crystal types, in which the longest axes were 507 and 230 Å. Using the smaller unit cell crystal, the structure was solved at 2.2 Å resolution. The asymmetric unit contained two tetrameric hemoglobin molecules. CONCLUSIONS The analyses revealed that αPro50 in the highland hemoglobin variant promoted a stable interaction between αHis45 and heme that was not seen in the αHis50 lowland variant. The αPro50 mutation also altered the nature of atomic contacts at the α1β2/α2β1 intersubunit interfaces. These results demonstrate how affinity-altering changes in intersubunit interactions can be produced by mutations at structurally remote sites.
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Affiliation(s)
- Noriko Inoguchi
- School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, United States of America
| | - Nobuhiro Mizuno
- Protein Crystal Analysis Division, Japan Synchrotron Radiation Research Institute, Sayo, Japan
| | - Seiki Baba
- Protein Crystal Analysis Division, Japan Synchrotron Radiation Research Institute, Sayo, Japan
| | - Takashi Kumasaka
- Protein Crystal Analysis Division, Japan Synchrotron Radiation Research Institute, Sayo, Japan
| | - Chandrasekhar Natarajan
- School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, United States of America
| | - Jay F. Storz
- School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, United States of America
| | - Hideaki Moriyama
- School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, United States of America
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19
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Regulation of blood oxygen transport in hibernating mammals. J Comp Physiol B 2017; 187:847-856. [DOI: 10.1007/s00360-017-1085-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Revised: 12/19/2016] [Accepted: 03/07/2017] [Indexed: 12/23/2022]
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20
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Fago A, Parraga DG, Petersen EE, Kristensen N, Giouri L, Jensen FB. A comparison of blood nitric oxide metabolites and hemoglobin functional properties among diving mammals. Comp Biochem Physiol A Mol Integr Physiol 2016; 205:35-40. [PMID: 27993597 DOI: 10.1016/j.cbpa.2016.12.013] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Revised: 12/09/2016] [Accepted: 12/12/2016] [Indexed: 01/01/2023]
Abstract
The ability of marine mammals to hunt prey at depth is known to rely on enhanced oxygen stores and on selective distribution of blood flow, but the molecular mechanisms regulating blood flow and oxygen transport remain unresolved. To investigate the molecular mechanisms that may be important in regulating blood flow, we measured concentration of nitrite and S-nitrosothiols (SNO), two metabolites of the vasodilator nitric oxide (NO), in the blood of 5 species of marine mammals differing in their dive duration: bottlenose dolphin, South American sea lion, harbor seal, walrus and beluga whale. We also examined oxygen affinity, sensitivity to 2,3-diphosphoglycerate (DPG) and nitrite reductase activity of the hemoglobin (Hb) to search for possible adaptive variations in these functional properties. We found levels of plasma and red blood cells nitrite similar to those reported for terrestrial mammals, but unusually high concentrations of red blood cell SNO in bottlenose dolphin, walrus and beluga whale, suggesting enhanced SNO-dependent signaling in these species. Purified Hbs showed similar functional properties in terms of oxygen affinity and sensitivity to DPG, indicating that reported large variations in blood oxygen affinity among diving mammals likely derive from phenotypic variations in red blood cell DPG levels. The nitrite reductase activities of the Hbs were overall slightly higher than that of human Hb, with the Hb of beluga whale, capable of longest dives, having the highest activity. Taken together, these results underscore adaptive variations in circulatory NO metabolism in diving mammals but not in the oxygenation properties of the Hb.
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Affiliation(s)
- Angela Fago
- Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.
| | | | - Elin E Petersen
- Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.
| | - Niels Kristensen
- Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.
| | - Lea Giouri
- Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.
| | - Frank B Jensen
- Department of Biology, University of Southern Denmark, 5230 Odense M, Denmark.
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Storz JF. Hemoglobin-oxygen affinity in high-altitude vertebrates: is there evidence for an adaptive trend? J Exp Biol 2016; 219:3190-3203. [PMID: 27802149 PMCID: PMC5091379 DOI: 10.1242/jeb.127134] [Citation(s) in RCA: 80] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
In air-breathing vertebrates at high altitude, fine-tuned adjustments in hemoglobin (Hb)-O2 affinity provide an energetically efficient means of mitigating the effects of arterial hypoxemia. However, it is not always clear whether an increased or decreased Hb-O2 affinity should be expected to improve tissue O2 delivery under different degrees of hypoxia, due to the inherent trade-off between arterial O2 loading and peripheral O2 unloading. Theoretical results indicate that the optimal Hb-O2 affinity varies as a non-linear function of environmental O2 availability, and the threshold elevation at which an increased Hb-O2 affinity becomes advantageous depends on the magnitude of diffusion limitation (the extent to which O2 equilibration at the blood-gas interface is limited by the kinetics of O2 exchange). This body of theory provides a framework for interpreting the possible adaptive significance of evolved changes in Hb-O2 affinity in vertebrates that have colonized high-altitude environments. To evaluate the evidence for an empirical generalization and to test theoretical predictions, I synthesized comparative data in a phylogenetic framework to assess the strength of the relationship between Hb-O2 affinity and native elevation in mammals and birds. Evidence for a general trend in mammals is equivocal, but there is a remarkably strong positive relationship between Hb-O2 affinity and native elevation in birds. Evolved changes in Hb function in high-altitude birds provide one of the most compelling examples of convergent biochemical adaptation in vertebrates.
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Affiliation(s)
- Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, NE 68588, USA
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