Purification, crystallization and preliminary X-ray analysis of haemoglobin I from the armoured catfish Liposarcus anisitsi

Liposarcus anisitsi is an armoured catfish that presents accessorial air oxygenation through a modified stomach, which allows this species to survive in waters with very low oxygen content. Analysis of its haemolysate has shown the presence of four haemoglobins; this work focuses on the main component, haemoglobin I. It has been crystallized in two different forms and X-ray diffraction data have been collected to 2.77 and 2.86 Å resolution using synchrotron radiation. Crystals were determined to belong to the space groups C2 and P2₁ and preliminary structural analysis revealed the presence of one tetramer in the asymmetric unit in both crystal forms. The structure was determined using a standard molecular-replacement technique.