STRUCTURE OF APO DUCK OVOTRANSFERRIN - THE STRUCTURES OF THE N-LOBE AND C-LOBE ARE IN THE OPEN FORM

The structure of apo duck ovotransferrin (APODOT) has been determined at a resolution of 4.0 Angstrom by the molecular replacement method us ing the structure of duck ovotransferrin (DOT) as the search model. Th e DOT structure contains two iron binding sites; one in the N-terminal lobe lying between domains N1 and N2 and one in the C-terminal lobe b etween domains C1 and C2. Both lobes have a closed structure, Models o f various forms of both the N and C lobes were used in the search. The final model was refined to give an R factor of 0.22. The comparison o f the structure of APODOT with that of DOT shows that both the N and t he C lobes are in an open form, where the N2 and C2 domains undergo la rge rigid-body rotations of 51.6 and 49.90 degrees relative to the N1 and C1 domains, respectively. The interface between the N and C lobes, which is formed by the N1-C1 contact in the core of the molecule does not change significantly. The DOT molecule may be described in terms of 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 as two other rigid bodies which, on the release of iron, move away from the static core of the molecule to form the open structure of APODOT.