Novel mechanism for high-altitude adaptation in hemoglobin of the Andean frogTelmatobius peruvianus

Abstract

In contrast to birds and mammals, no information appears to be available on the molecular adaptations for O2 transport in high-altitude ectothermic vertebrates. We investigated Hb of the aquatic Andean frog Telmatobius peruvianus from 3,800-m altitude as regards isoform differentiation, sensitivity to allosteric cofactors, and primary structures of the ␣-and ␤-chains, and we carried out comparative O2-binding measurements on Hb of lowland Xenopus laevis. The three T. peruvianus isoHbs show similar functional properties. The high O2 affinity of the major component results from an almost complete obliteration of chloride sensitivity, which correlates with two ␣-chain modifications: blockage of the NH2-terminal residues and replacement by nonpolar Ala of polar residues Ser and Thr found at position ␣131(H14) in human and X. leavis Hbs, respectively. The data indicate adaptive significance of ␣-chain chloride-binding sites in amphibians, in contrast to human Hb where chloride appears mainly to bind in the cavity between the ␤-chains. The findings are discussed in relation to other strategies for high-altitude adaptations in amphibians.amphibians; chloride binding; hypoxia; organic phosphates; oxygen transport HOW IS OXYGEN TRANSPORT to metabolizing tissues secured at high altitude? In contrast to intensive investigations in birds and mammals (7,39,59), the molecular strategies for O 2 transport in high-altitude ectothermic vertebrates remain unexplored, despite greater variations in environmental conditions (temperature, pH, O 2 tension, etc.) and lesser capacities for homeostatic regulation of internal physical and chemical conditions compared with homeothermic vertebrates and a long-standing interest in high-altitude aquatic amphibians (1, 24).The anuran genus Telmatobius (that variously is referred to as frogs or toads) occurs in the Andes mountains at altitudes from 2,000 to over 4,000 m (14) where aerial O 2 tensions fall from ϳ159 mmHg at sea level to ϳ92 mmHg. The hypoxic stress is compounded in aquatic species, particularly at night when photosynthetic activity in the ponds ceases (21). T. culeus found in Lake Titicaca at 3,812 m has reduced, poorly developed lungs but exhibits compensatory physiological and behavioral adaptations (24) that include an "oversized," folded skin, which is penetrated by cutaneous capillaries and ventilated by "bobbing" behavior under hypoxia, and small erythrocytes and higher erythrocyte counts, blood-O 2 affinities, and O 2 -carrying capacities than anurans living at sea level (24). Subspecies of Bufo spinulosus living at sea level and at 3,100 to 4,100 m in the Andes analogously exhibit increasing blood-O 2 affinities with altitude (43).The O 2 affinity of blood is a product of the intrinsic O 2 affinity of the Hb molecules and the erythrocytic effectors that modulate Hb-O 2 affinity. Compared with mammals that use 2,3-diphosphoglycerate (DPG) and fish that use ATP (often in conjunction with the more potent effector guanosine triphosphate) (60) as organic O 2 -affinity modulat...

Gene Duplication and the Evolution of Hemoglobin Isoform Differentiation in Birds

“…For each individual specimen, Hb isoform composition was characterized by means of alkaline PAGE and/or thin layer isoelectric focusing (PhastSystem, GE Healthcare Biosciences). Depending on the species, the HbA and HbD isoforms were separated by fast protein liquid chromatography (FPLC), DEAE anion-exchange chromatography, CM-Sepharose cation-exchange chromatography, and/or preparative electrofocusing, as described previously (11,36,43,44). The separate isoHbs were further stripped of organic phosphate and other ions by passing the samples through a mixed bed resin column (MB-1 AG501-X8; Bio-Rad) using FPLC.…”

Genetic differences in hemoglobin function between highland and lowland deer mice

“…This raises questions about the molecular basis of the reduced oxygenation-linked Cl -binding of deer mouse Hb. In human embryonic Hbs (Hb Portland and Hb Gower I) (Zheng et al, 1999) and in the major isoHb of the Andean frog Telmatobius peruvianus (Weber et al, 2002) drastic reductions in Cl -sensitivity correlate with substitutions of non-polar residues for 131(H14)Ser, which may reflect the elimination of a specific oxygenation-linked Cl -binding site. The low number of oxygenation-linked Cl -ions in deer mouse Hb is unexpected, given the presence of 1(NA1)Val, 131(H14)Ser and 82(EF6)Lys.…”

Genomic insights into adaptation to high-altitude environments

“…Changes in oxygenbinding affinity of Hb proteins can have major effects on oxygen transport, especially under hypoxic conditions, and the increased Hb oxygen affinity of high-altitude animals is arguably the most famous adaptation to high altitude (reviewed in Perutz, 1983;Bouverot, 1985;Hochachka and Somero, 2002;Weber, 2007;Storz and Moriyama, 2008). Hb oxygen affinity is the product of the intrinsic ability of Hb molecules to bind oxygen and other erythrocytic cofactors, and the intracellular concentration of these cofactors (Weber et al, 2002;Weber and Fago, 2004;Weber, 2007;Storz and Moriyama, 2008). A number of erythrocytic compounds are known to influence Hb oxygen affinity in vertebrates.…”

“…Much of what is known about the genetic basis of high-altitude adaptation in natural populations comes from studies that have taken a 'candidate gene' approach, and many of these studies have focused on sequence variation in hemoglobin genes. Several of these have become well-known case studies of the genetics of adaptation (Snyder, 1978(Snyder, , 1985Snyder et al, 1982Snyder et al, , 1988Chappell and Snyder, 1984;Jessen et al, 1991;Weber et al, 2002;Storz et al, 2007Storz et al, , 2009Storz et al, , 2010a, but many other physiological traits may be as important as blood oxygen affinity in determining lifetime reproductive success in high-altitude environments. These physiological parameters are often complex traits with a polygenic basis.…”