2peg

From Proteopedia

Revision as of 10:50, 23 January 2008

Crystal structure of Trematomus bernacchii hemoglobin in a partial hemichrome state

Overview

Spontaneous autoxidation of tetrameric hemoglobins leads to the formation, of Fe (III) forms, whose physiological role is not fully understood. Here, we report structural characterization by EPR of the oxidized states of, tetrameric hemoglobins isolated from the Antarctic fish species Trematomus, bernacchii, Trematomus newnesi, and Gymnodraco acuticeps, as well as the, X-ray crystal structure of oxidized Trematomus bernacchii hemoglobin, re-determined at high resolution. The oxidation of these hemoglobins leads, to formation of states that were not usually detected in previous analyses, of tetrameric hemoglobins. In addition to the commonly found aquo-met and, hydroxy-met species, EPR analyses show that two distinct hemichromes, co-exist at physiological pH, referred to as hemichromes I and II, respectively. Together with the high-resolution crystal structure (1.5 A), of T. bernacchii and a survey of data available for other heme proteins, hemichrome I was assigned by X-ray crystallography and by EPR as a bis-His, complex with a distorted geometry, whereas hemichrome II is a less, constrained (cytochrome b5-like) bis-His complex. In four of the five, Antartic fish hemoglobins examined, hemichrome I is the major form. EPR, shows that for the cathodic hemoglobin component of T. newnesi (HbCTn), the amount of hemichrome I is substantially reduced. In addition, the, concomitant presence of a penta-coordinated high-spin Fe (III) species, never reported before for a wild-type tetrameric hemoglobin, was detected., A molecular modeling investigation demonstrates that the presence of the, bulkier Ile in position 67beta in HbCTn in place of Val as in the other, four Hbs impairs the formation of hemichrome I, thus favoring the, formation of the ferric penta-coordinated species. Altogether the present, data show that ferric states commonly associated with monomeric and, dimeric hemoglobins are also found in tetrameric hemoglobins.

About this Structure

2PEG is a Protein complex structure of sequences from Trematomus bernacchii with and as ligands. Full crystallographic information is available from OCA.

Reference

Structural characterization of ferric hemoglobins from three Antarctic fish species of the suborder Notothenioidei., Vergara A, Franzese M, Merlino A, Vitagliano L, Verde C, di Prisco G, Lee HC, Peisach J, Mazzarella L, Biophys J. 2007 Jun 1;. PMID:17545238

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