Transferrins coordination environment

The transferrins belong to the iron-tyrosinate group of proteins discussed in Section 62.1.5.5.2. Charge transfer from phenolate ligands to Fem accounts for the salmon-pink colour of transferrin. The detailed coordination environment of the iron in transferrin is not known with certainty, as... 

Fig. 29.3 (a) The structure of human serum transferrin determined by X-ray diffraction (PDB code 1D3K). The protein chain is shown in ribbon representation and the coordination sphere of the Fe ion is depicted in ball (for Fe ) and stick (for the amino acid residues and [C03] ion) representations, (b) An enlargement of the coordination environment of Fe. Colour code Fe, green N, blue O, red C, grey, (c) Schematic representation of the Fe binding site in transferrin the coordinated [ 03] points towards the positively charged Arg residue and the A -terminus of a helix. 

The ESR spectra of copper serum transferrins and ovotransferrins were characteristic of Cu2+ in an environment which has axial symmetry. The coordination appeared to be square planer based on the similarity to ESR spectra for known complexes of this symmetry. The extra-hf splitting of the gJ-peak (Fig. 10) was interpreted as direct evidence for coordination of the copper to nitrogen atoms. Both Aasa et al. (7) and Windle et al. (137) concluded that the copper was bound to two or more nitrogen atoms. 

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