Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 107, Issue 32, Pages 14274-14279Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1006756107
Keywords
cytoglobin; gene family evolution; globin; hagfish; lamprey
Categories
Funding
- National Science Foundation
- National Institutes of Health/National Heart, Lung, and Blood Institute
- Fondo Nacional de Desarrollo Cientifico y Tecnologico (FONDECYT) [11080181]
- Programa Bicentenario en Ciencia y Tecnologia [PSD89]
- Concurso Estadia Jovenes Investigadores en el Extranjero from the Universidad Austral de Chile
- Microsoft Corporation
- Division Of Integrative Organismal Systems
- Direct For Biological Sciences [0949931] Funding Source: National Science Foundation
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Natural selection often promotes evolutionary innovation by coopting preexisting genes for new functions, and this process may be greatly facilitated by gene duplication. Here we report an example of cooptive convergence where paralogous members of the globin gene superfamily independently evolved a specialized O(2) transport function in the two deepest branches of the vertebrate family tree. Specifically, phylogenetic evidence demonstrates that erythroid-specific O(2) transport hemoglobins evolved independently from different ancestral precursor proteins in jawed vertebrates (gnathostomes) and jawless fish (cyclostomes, represented by lamprey and hagfish). A comprehensive phylogenetic analysis of the vertebrate globin gene superfamily revealed that the erythroid hemoglobins of cyclostomes are orthologous to the cytoglobin protein of gnathostome vertebrates, a hexacoordinate globin that has no O(2) transport function and that is predominantly expressed in fibroblasts and related cell types. The phylogeny reconstruction also revealed that vertebrate-specific globins are grouped into four main clades: (i) cyclostome hemoglobin + cytoglobin, (ii) myoglobin + globin E, (iii) globin Y, and (iv) the alpha- and beta-chain hemoglobins of gnathostomes. In the hemoglobins of gnathostomes and cyclostomes, multi-subunit quaternary structures provide the basis for cooperative O(2) binding and allosteric regulation by coupling the effects of ligand binding at individual subunits with interactions between subunits. However, differences in numerous structural details belie their independent origins. This example of convergent evolution of protein function provides an impressive demonstration of the ability of natural selection to cobble together complex design solutions by tinkering with different variations of the same basic protein scaffold.
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