Crystallization of sheep (Ovis aries) and goat (Capra hircus) haemoglobins under unbuffered low-salt conditions

Haemoglobin is a tetrameric protein that plays a vital role in the transport of oxygen from the lungs to the tissues and of carbon dioxide back to the lungs. Even though a large amount of work has already been performed in this area, the study of the haemoglobin structures of avian and mammalian species is rather incomplete. Efforts are being made to understand the salient features of the species mentioned above. Here, whole blood plasma was collected from sheep and goat and purified by anion-exchange chromatography; the haemoglobins were crystallized by the hanging-drop vapour-diffusion method under unbuffered low-salt conditions using PEG 3350 as a precipitant. Data collection was carried out using a MAR345 image-plate detector system. Sheep haemoglobin crystallizes in the orthorhombic space group P2₁2₁2₁ with one whole biological molecule (α₂β₂) in the asymmetric unit, with unit-cell parameters a = 60.231, b = 70.695, c = 131.479 Å. In contrast, goat haemoglobin crystallizes in the triclinic system with two biological molecules (α₂β₂) in the unit cell. The unit-cell parameters are a = 53.103, b = 69.382, c = 96.098 Å, α = 110.867, β = 91.133, γ = 109.437°.