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Biochem Biophys Res Commun. 2014 Jul 18;450(1):36-41. doi: 10.1016/j.bbrc.2014.05.062. Epub 2014 May 22.

Structural studies on a low oxygen affinity hemoglobin from mammalian species: sheep (Ovis aries).

Author information

  • 1Centre of Advanced Study in Crystallography and Biophysics, University of Madras, Guindy Campus, Chennai 600 025, India. Electronic address: neelagandank@bii.a-star.edu.sg.
  • 2Centre of Advanced Study in Crystallography and Biophysics, University of Madras, Guindy Campus, Chennai 600 025, India.
  • 3Centre of Advanced Study in Crystallography and Biophysics, University of Madras, Guindy Campus, Chennai 600 025, India. Electronic address: mnpsy@hotmail.com.

Abstract

Hemoglobin (Hb) is in equilibrium between low affinity Tense (T) and high affinity Relaxed (R) states associated with its unliganded and liganded forms, respectively. Mammalian species can be classified into two groups on the basis of whether they express 'high' and 'low' oxygen affinity Hbs. Although Hbs from former group have been studied extensively, a limited number of structural studies have been performed for the low oxygen affinity Hbs. Here, the crystal structure of low oxygen affinity sheep methemoglobin (metHb) has been determined to 2.7 Å resolution. Even though sheep metHb adopts classical R state like quaternary structure, it shows localized quaternary and tertiary structural differences compared with other liganded Hb. The critical group of residues in the "joint region", shown as a major source of quaternary constraint on deoxyHb, formed unique interactions in the α1β2/α2β1 interfaces of sheep metHb structure. In addition, the constrained β subunits heme environment and the contraction of N-termini and A-helices of β subunits towards the molecular dyad are observed for sheep metHb structure. These observations provide the structural basis for a low oxygen affinity and blunt response to allosteric effector of sheep Hb.

KEYWORDS:

Allosteric mechanism; Crystal structure; Hemoglobin; Low oxygen affinity; Sheep

PMID:
24858681
DOI:
10.1016/j.bbrc.2014.05.062
[PubMed - indexed for MEDLINE]
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