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J. Biol. Chem., Vol. 280, Issue 44, 36754-36761, November 4, 2005

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Thermoglobin, Oxygen-avid Hemoglobin in a Bacterial Hyperthermophile^*

JJ L. Miranda1, David H. Maillett2, Jayashree Soman, and John S. Olson

From the Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138 and the Department of Biochemistry and Cell Biology and the Keck Center for Computational Biology, Rice University, Houston, Texas 77005

The hemoglobin family of proteins, ubiquitous in all domains of life, evolved from an ancestral protein of primordial function to extant hemoglobins that perform a myriad of functions with diverged biochemical properties. Study of homologs in bacterial hyperthermophiles may shed light on both mechanisms of adaptation to extreme conditions and the nature of the ancestral protein. A hemoglobin was identified in Aquifex aeolicus, cloned, recombinantly expressed, purified, and characterized. This hemoglobin is monomeric, resistant to thermal and chemical denaturation, pentacoordinate in the ferrous deoxygenated state, and oxygen-avid. The oxygen equilibrium dissociation constant is approximately 1 nM at room temperature, due in part to a hydrogen bond between the bound ligand and a tyrosine residue in the distal pocket. These biochemical properties of A. aeolicus thermoglobin, AaTgb, may have been shared by the ancestral hemoglobin, thus suggesting possible primordial functions and providing a starting point for consequent evolution of the hemoglobin family.

Received for publication, May 31, 2005 , and in revised form, August 30, 2005.

^* This work was supported by a National Science Foundation graduate research fellowship (to J. L. M.), National Institutes of Health Grants GM 35649 (to J. S. O.) and HL 47020 (to J. S. O.) and Robert A. Welch Foundation Grant C-0612 (to J. S. O.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

² Present address: Dept. of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA 15213.

¹ To whom correspondence should be addressed: Dept. of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 250 Longwood Ave., Boston, MA 02115. Tel.: 617-432-5605; Fax: 617-432-5600; E-mail: jjmirand{at}fas.harvard.edu.

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