Oxygenation properties and isoform diversity of snake hemoglobins.
Available data suggest that snake hemoglobins (Hbs) are characterized by a combination of unusual structural and functional properties relative to the Hbs of other amniote vertebrates, including oxygenation-linked tetramer-dimer dissociation. However, standardized comparative data are lacking for snake Hbs, and the Hb isoform composition of snake red blood cells has not been systematically characterized. Here we present the results of an integrated analysis of snake Hbs and the underlying α- and β-type globin genes to characterize 1) Hb isoform composition of definitive erythrocytes, and 2) the oxygenation properties of isolated isoforms as well as composite hemolysates. We used species from three families as subjects for experimental studies of Hb function: South American rattlesnake, Crotalus durissus (Viperidae); Indian python, Python molurus (Pythonidae); and yellow-bellied sea snake, Pelamis platura (Elapidae). We analyzed allosteric properties of snake Hbs in terms of the Monod-Wyman-Changeux model and Adair four-step thermodynamic model. Hbs from each of the three species exhibited high intrinsic O2 affinities, low cooperativities, small Bohr factors in the absence of phosphates, and high sensitivities to ATP. Oxygenation properties of the snake Hbs could be explained entirely by allosteric transitions in the quaternary structure of intact tetramers, suggesting that ligation-dependent dissociation of Hb tetramers into αβ-dimers is not a universal feature of snake Hbs. Surprisingly, the major Hb isoform of the South American rattlesnake is homologous to the minor HbD of other amniotes and, contrary to the pattern of Hb isoform differentiation in birds and turtles, exhibits a lower O2 affinity than the HbA isoform.
School of Biological Sciences, University of Nebraska, Lincoln, Nebraska; jstorz2@unl.edu.
Jay F
JF
Storz
School of Biological Sciences, University of Nebraska, Lincoln, Nebraska;
Chandrasekhar
C
Natarajan
School of Biological Sciences, University of Nebraska, Lincoln, Nebraska;
Hideaki
H
Moriyama
Department of Biochemistry, Molecular Biology, Entomology, and Plant Pathology, Mississippi State University, Starkville, Mississippi; Institute for Genomics, Biocomputing, and Biotechnology, Mississippi State University, Mississippi State, Mississippi; and.
Federico G
FG
Hoffmann
Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
Tobias
T
Wang
Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
Angela
A
Fago
Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
Hans
H
Malte
Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
Johannes
J
Overgaard
Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark.
Roy E
RE
Weber
D000595:Amino Acid Sequence; D000818:Animals; D014644:Genetic Variation; D006454:Hemoglobins / Q000737:chemistry* / Q000235:genetics*; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D020033:Protein Isoforms; D012911:Snakes / Q000145:classification* / Q000502:physiology*; D013045:Species Specificity; D013329:Structure-Activity Relationship
D006454:Hemoglobins; D020033:Protein Isoforms; D010100:Oxygen
Crotalus; Pelamis; allosteric regulation; blood-oxygen transport; python