Nagaraj Shobana

Introduction: Angora goats are a distinct breed that differs significantly from common goats and shares a similar appearance to sheep. In Angora goats, only the level of glutathione (GSH) is elevated during under-stimulated conditions, as well as after the period of hypoxic stress; however, no changes are found in 2,3-diphosphoglycerate (2,3-DPG) levels, which are commonly present in the red blood cells (RBCs) of most mammals. We chose the Angora goat for our investigation because no previous studies have been conducted on the structural and functional aspects of hemoglobin (Hb). In addition, no sequence or structural information is currently available in any database. Methods: Angora goat Hb was isolated and purified by anion-exchange chromatography, followed by crystallization using various methods. X-ray data collection for Angora goat Hb was performed under a liquid nitrogen cryo-stream using a Bruker D8 Venture Bio Photon III 28-pixel array area detector system. Results: Good diffracting crystals were obtained using the hanging-drop vapor-diffusion method with polyethylene glycol (PEG) 3350 as the precipitant in water, without the addition of any salt or buffer. The Angora goat Hb diffracted to a resolution of 1.85 Å, and the structure solution was obtained by the molecular replacement method, using the structure of domestic goat Hb as the starting model. Discussion: The solved structure of Angora goat crystallized in the monoclinic space group P21, consisting of one whole biological molecule in the asymmetric unit, with unit cell dimensions of a = 52.08 Å, b = 76.70 Å, c = 74.08 Å, and β = 91.77 °. The solvent content and Matthews coefficient (Vm) for the Angora goat Hb are 49.05% and 2.41 Å3/Da, respectively, and are within the normal range for protein crystals. Conclusion: Purification, crystallization, and preliminary X-ray diffraction studies of Angora goat Hb were performed successfully. Structural refinement and biophysical characterization of Angora goat Hb are in progress in the absence and presence of GSH and 2,3-DPG.

Crystal structures of hemoglobin (Hb) from two flightless birds, ostrich (Struthio camelus) and turkey (Meleagris gallopova), were determined. The ostrich Hb structure was solved to a resolution of 2.22 Å, whereas two forms of turkey Hb were solved to resolutions of 1.66 Å (turkey monoclinic structure; TMS) and 1.39 Å (turkey orthorhombic structure; TOS). Comparison of the amino-acid sequences of ostrich and turkey Hb with those from other avian species revealed no difference in the number of charged residues, but variations were observed in the numbers of hydrophobic and polar residues. Amino-acid-composition-based computation of various physical parameters, in particular their lower inverse transition temperatures and higher average hydrophobicities, indicated that the structures of ostrich and turkey Hb are likely to be highly ordered when compared with other avian Hbs. From the crystal structure analysis, the liganded state of ostrich Hb was confirmed by the presence of an oxygen molecule between the Fe atom and the proximal histidine residue in all four heme regions. In turkey Hb (both TMS and TOS), a water molecule was bound instead of an oxygen molecule in all four heme regions, thus confirming that they assumed the aqua-met form. Analysis of tertiary- and quaternary-structural features led to the conclusion that ostrich oxy Hb and turkey aqua-met Hb adopt the R-/R_H-state conformation.

Mice (Mus musculus) are nocturnal small animals belonging to the rodent family that live in burrows, an environment in which significantly high CO₂ levels prevail. It is expected that mouse hemoglobin (Hb) plays an important role in their adaptation to living in such a high-CO₂ environment, while many other species cannot. In the present study, mouse Hb was purified and crystallized at a physiological pH of 7 in the orthorhombic space group P2₁2₁2₁; the crystals diffracted to 2.8 Å resolution. The primary amino-acid sequence and crystal structure of mouse Hb were compared with those of mammalian Hbs in order to investigate the structure–function relationship of mouse Hb. Differences were observed from guinea pig Hb in terms of amino-acid sequence and from cat Hb in overall structure (in terms of r.m.s.d.). The difference in r.m.s.d. from cat Hb may be due to the existence of the molecule in a conformation other than the R-state. Analysis of tertiary- and quaternary-structural features, the α1β2 interface region and the heme environment without any ligands in all four heme groups showed that mouse methemoglobin is in an intermediate state between the R-state and the T-state that is much closer to the R-state conformation.