CRYSTALLOGRAPHIC STRUCTURES OF DIFERRIC AND APO DUCK OVOTRANSFERRINS. A. Rawas, H. Muirhead and J. Williams, Department of Biochemistry and Molecular Recognition Centre, University of Bristol, Bristol BS8 1TD, UK.

The structures of Diferric Duck Ovotransferrin (DOT) and Apo Duck Ovotransferrin ( APODOT ) have been determined by the molecular replacement method. The main differences between the known diferric transferrin structures lie in the relative orientations of the N- and C-lobes with respect to each other. In the DOT structure the large aromatic side chain Phe322 in the N-lobe packs against the conserved residue Gly387 in the C-lobe. This interaction is at the centre of the interface between the two lobes and could play a crucial role in determining their relative orientation.

The DOT molecule can be described as three rigid bodies; the N1 and C1 domains as one rigid body forming the static core of the molecule and the N2 and C2 domains forming two other rigid bodies which move away from the N1 and C1 domains ( the static core of the molecule ) to form the open structure of APODOT. The structure of APODOT shows that both the N- and the C-lobes are in the open form, where the N2 and C2 domains undergo large rotations as rigid bodies of 51.6( and 49.9( respectively relative to the N1 and C1 domains.