Lactoferrin connecting peptide

The two lobes are joined by a short connecting peptide, which is the only covalent link between them. This peptide varies between different transferrins, both in length (7 to 14 residues—see Section III.C) and in conformation in lactoferrin, it is 12 residues long and forms a three-turn helix, whereas in serum transferrin it is 14 residues long and has a much less regular structure. 

Fig. 3. Domain organization of transferrins. The N-terminal lobe (above) is divided into domains N1 and N2, and the C-terminal lobe (below), into domains Cl and C2. The two lobes are related by a screw axis, a rotation of -180°, and a translation of 25 A. The two iron sites are identified with closed circles. The connecting peptide that joins the two lobes is helical in lactoferrin (solid line) and less regular in transferrin (dashed line).

Fig. 4. Ribbon diagram of human diferric lactoferrin, showing the organization of the molecule, with the N-lobe above and C-lobe below. The four domains (Nl, N2, Cl, C2), the interlobe connecting peptide (H), and the C-terminal helix (C) are indicated. The glycosylation sites in various transferrins are shown by triangles and numbered (1, human transferrin 2, rabbit transferrin 3, human lactoferrin 4, bovine lactoferrin 5 chicken ovotransferrin). The interdomain backbone strands in each lobe can be seen behind the iron atoms. Adapted from Baker et al. (82), with permission.

The one-letter code for amino acids is used (C, Cys P, Pro etc.). Alignment on either side of the connecting peptide iB based on the lactoferrin and transferrin 3D BtructureB. The last helix in the N-lobe and firBt /3-strand in the C-lobe are indicated. Cys and Pro residues are in boldface. 

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