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J. Biol. Chem., Vol. 276, Issue 29, 27415-27423, July 20, 2001

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Hagfish Hemoglobins
STRUCTURE, FUNCTION, AND OXYGEN-LINKED ASSOCIATION^*

Angela Fago, Laura Giangiacomo^§, Rossana D'Avino^¶, Vito Carratore^¶, Mario Romano^¶, Alberto Boffi^§, and Emilia Chiancone^§

From the  Department of Zoophysiology, University of Aarhus, Bldg. 131, Universitetsparken, DK 8000 Aarhus C, Denmark, the ^§ Consiglio Nazionale delle Ricerche Center of Molecular Biology and Department of Biochemical Sciences, University "La Sapienza" P.le Aldo Moro 5, Roma 00185, Italy, and the ^¶ Consiglio Nazionale delle Ricerche Institute of Protein Biochemistry and Enzymology, Via Marconi 10, Napoli 80125, Italy

Cyclostomes, hagfishes and lampreys, contain hemoglobins that are monomeric when oxygenated and polymerize to dimers or tetramers when deoxygenated. The three major hemoglobin components (HbI, HbII, and HbIII) from the hagfish Myxine glutinosa have been characterized and compared with lamprey Petromyzon marinus HbV, whose x-ray crystal structure has been solved in the deoxygenated, dimeric state (Heaslet, H. A., and Royer, W. E., Jr. (1999) Structure 7, 517-526). Of these three, HbII bears the highest sequence similarity to P. marinus HbV. In HbI and HbIII the distal histidine is substituted by a glutamine residue and additional substitutions occur in residues located at the deoxy dimer interface of P. marinus HbV. Infrared spectroscopy of the CO derivatives, used to probe the distal pocket fine structure, brings out a correlation between the CO stretching frequencies and the rates of CO combination. Ultracentrifugation studies show that HbI and HbIII are monomeric in both the oxygenated and deoxygenated states under all conditions studied, whereas deoxy HbII forms dimers at acidic pH values, like P. marinus HbV. Accordingly, the oxygen affinities of HbI and HbIII are independent of pH, whereas HbII displays a Bohr effect below pH 7.2. HbII also forms heterodimers with HbIII and heterotetramers with HbI. The functional counterparts of heteropolymer formation are cooperativity in oxygen binding and the oxygen-linked binding of protons and bicarbonate. The observed effects are explained on the basis of the x-ray structure of P. marinus HbV and the association behavior of site-specific mutants (Qiu, Y., Maillett, D. H., Knapp, J., Olson, J. S., and Riggs, A. F. (2000) J. Biol. Chem. 275, 13517-13528).

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