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Structure and function of the Gondwanian hemoglobin of Pseudaphritis urvillii, a primitive notothenioid fish of temperate latitudes

¹ Institute of Protein Biochemistry (IBP), National Research Council (CNR), I-80125 Naples, Italy
² Department of Chemistry, University of Florence, I-50019 Sesto Fiorentino, Florence, Italy
³ Institute of Biochemistry and Clinical Biochemistry and CNR Institute of Chemistry of Molecular Recognition, Catholic University, I-00168 Rome, Italy
⁴ Australian Antarctic Division, Kingston, Tasmania 7050, Australia

(RECEIVED May 13, 2004; FINAL REVISION June 25, 2004; ACCEPTED July 2, 2004)

The suborder Notothenioidei dominates the Antarctic ichthyofauna. The non-Antarctic monotypic family Pseudaphritidae is one of the most primitive families. The characterization of the oxygen-transport system of euryhaline Pseudaphritis urvillii is herewith reported. Similar to most Antarctic notothenioids, this temperate species has a single major hemoglobin (Hb 1, over 95% of the total). Hb 1 has strong Bohr and Root effects. It shows two very uncommon features in oxygen binding: At high pH values, the oxygen affinity is exceptionally high compared to other notothenioids, and subunit cooperativity is modulated by pH in an unusual way, namely the curve of the Hill coefficient is bell-shaped, with values approaching 1 at both extremes of pH. Molecular modeling, electronic absorption and resonance Raman spectra have been used to characterize the heme environment of Hb 1 in an attempt to explain these features, particularly in view of some potentially important nonconservative replacements found in the primary structure. Compared to human HbA, no major changes were found in the structure of the proximal cavity of the -chain of Hb 1, although an altered distal histidyl and heme position was identified in the models of the -chain, possibly facilitated by a more open heme pocket due to reduced steric constraints on the vinyl substituent groups. This conformation may lead to the hemichrome form identified by spectroscopy in the Met state, which likely fulfils a potentially important physiological role.

Keywords: Antarctica; fish; Pseudaphritis urvillii; hemoglobin; Bohr/Root effects; evolution; electronic absorption spectroscopy; Resonance Raman spectroscopy; molecular modeling

Article published online ahead of print. Article and publication date are at http://www.proteinscience.org/cgi/doi/10.1110/ps.04861504.

Reprint requests to: Guido di Prisco, IBP-CNR, Via Marconi 12, I-80125 Naples, Italy; e-mail: g.diprisco{at}ibp.cnr.it; fax: +39-081-593-6689.

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