Jaimohan, S M and Naresh, M D and Mandal, A B (2021) Parakeet Hemoglobin - Its Crystal Structure and Oxygen Affinity in Relation to Some Avian Hemoglobins. Protein and Peptide Letters, 28 (1). pp. 18-30. ISSN 0929-8665

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Background: ``Avians'' often show efficient oxygen management to meet the demands of their metabolism. Hemoglobin, a transporter protein consists of four non-covalently linked subunits contain haem binding hydrophobic pocket serves as a site of allosteric cooperativity. The physiology and anatomy of both mammals and avian are functionally different, in birds, the respiratory system formed by small air sacs that serve as tidal ventilation for the lungs and have no significant exchange across their cells. Parakeet (Psittacula krameri) a tropical and non-migrating species and it is easily adapted to living in disturbed habitat. The sequence analysis reveals that alpha and beta chain of parakeet hemoglobin highly similar grey lag goose and bar headed goose hemoglobin respectively. Thus it has been tempted us to study in to analyzing the sequence and structural comparison of this hemoglobin to find out the physiological capabilities of parakeet hemoglobin. Objective: The structure determination studies of parakeet hemoglobin by X-ray diffraction. The sequence and structure are compared with goose, chicken and human Hb, emphasizing the role of amino acids in the subunit contacts that facilitate survival by low oxygen demand. Methods: The Hb was purified and crystallized by hanging drop vapor diffusion method using polyethylene glycol (PEG) 3350 and sodium phosphate buffer. X-ray diffracted data set was collected at 3 angstrom resolution, the data was processed in Automar and molecular replacement, refinements, model building was carried out in CCP4i program package. The final refined model was deposited in protein data bank with accession id 2zfb. Results: The tertiary structure of Parakeet Hb is compared with the met form of BHG Hb (1c40) and oxy form of GLG (1faw) and oxy form of human Hbs (1hho). Superimposing parakeet Hb alpha(1)beta(1) subunit with `R' state human Hb shows an r.m.s.d of 0.98 angstrom and for BHG and GLG Hb, the r.m.s.d shows 0.72 and 0.61 angstrom. The replacement of alpha 115Asp in parakeet Hb as against the alpha 115Glu in human Hb results in the movement of GH corners. The amino acid proline at alpha 50 present only in Parakeet Hb and Chicken HbD and not present in any other avian family which includes human Hb. The residue alpha 78Thr located in EF corner loop region, which slightly diverge when superimposing with human and BHG Hb and also replacement of alpha 113Asn present only in Parakeet Hb placed near the FG helix corner. Conclusion: The present study describes the structure determination of parakeet hemoglobin and its structural features to understand its oxygen affinity characteristics. The crystals were obtained by buffered low-salt conditions, like those of chicken HbD, carbonmonoxy and cyanomet human Hb. The present study reveals several interesting and unique modifications in the finer aspects of the quaternary structure of parakeet Hb, which are involved in oxygen affinity characteristics and the alpha(1)beta(1) subunit contacts. Crystallization of parakeet Hb with allosteric effectors like Inositol pentaphosphate may bring further understanding of the influence of physiological and environmental factors on the quaternary structure.

Item Type: Article
Subjects: Engineering Materials
Depositing User: Bidhan Chaudhuri
Date Deposited: 10 Dec 2021 10:14
Last Modified: 10 Dec 2021 10:14
URI: http://cgcri.csircentral.net/id/eprint/5204

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