What do you do with the DNA sequence of an animal that has been extinct for tens of thousands of years? Well, if you are on the team of Professor Kevin Campbell (University of Manitoba, Canada), you go for the blood; specifically, the hemoglobin. In a study published in Nature Genetics (1), Professor Campbell’s team reports that they have successfully expressed the mammoth hemoglobin protein using the sequence from a 43,000 year-old mammoth specimen.
As it turns out, mammoth hemoglobin is pretty interesting, at least from an evolutionary biology/paleogenetic point of view. When the polypeptides from the α- and β-like globin genes of the mammoth were compared to those of the African (Loxodonta africana) and Asian (Elaphas maximus) elephants, there were only a few amino acids different in the genes, but these changes had pretty spectacular results on the physiochemical properties of the mammoth hemoglobin.
Hemoglobin binds and carries O2 in the blood. Hemoglobin’s affinity for O2 increases as temperature decreases. Because the process of releasing O2 (heme deoxygenation) is endothermic, the ability of hemoglobin to release, or off load, the O2 to the cells that need it is greatly reduced at lower temperatures. This means that heme deoxygenation results in an overall loss of heat that would be costly to an arctic mammal.
So how did an African-derived lineage come to survive so well in the arctic? Well, it turns out that the altered residues in the mammoth hemoglobin resulted a lower oxygenation enthalpy (Δh) compared to that of the Asian elephant. While mammals general have a Δh that cause small increases in temperature to result in large decreases in hemoglobin- O2 affinity, which helps site-specific O2 delivery to warmer exercising muscles, this is not the case for mammoth hemoglobin. Instead, Professor Campbell’s team found that the effects of changes in temperature on a mammoth’s hemoglobin affinity for O2 would be greatly reduced, thereby allowing the hemoglobin to release the O2 more easily at lower temperatures. This would have been an enormous energy advantage for the arctic-dwelling mammoth.
As if all this wasn’t cool enough on its own, there is also the wow factor of holding a plate of cells that are expressing a protein from the blood of an animal that last roamed the earth over 43,000 years ago. Just thinking about that gives me chills.
Campbell KL, Roberts JE, Watson LN, Stetefeld J, Sloan AM, Signore AV, Howatt JW, Tame JR, Rohland N, Shen TJ, Austin JJ, Hofreiter M, Ho C, Weber RE, & Cooper A (2010). Substitutions in woolly mammoth hemoglobin confer biochemical properties adaptive for cold tolerance. Nature genetics PMID: 20436470