New insight into the haemoglobin superfamily: preliminary crystallographic characterization of human cytoglobin

Human cytoglobin, present in almost all tissue types, is a newly identified member of the Hb superfamily. A double mutant, having both cysteines replaced by serines, has been overexpressed in Escherichia coli, purified and crystallized. A highly redundant SAD data set has been collected at the haem Fe-atom absorption edge (lambda=1.720 Angstrom) to 2.60 Angstrom resolution. The crystals belong to the orthorhombic P2(1)2(1)2(1) space group, with unit-cell parameters a=46.8, b=73.1, c=98.9Angstrom and two molecules per asymmetric unit. The anomalous difference Patterson map clearly reveals the position of the haem Fe-atom sites, thus paving the way for SAD structure determination.