Disulfide bonding, transferrins

In common with most laboratories engaged in fundamental research on proteins, our laboratory has studied the denaturation and renaturation of proteins. Many of these studies have been with the two related homologous iron-binding proteins, human serum transferrin and chicken ovotransferrin. Earlier studies showed that on the binding of iron these proteins were greatly stabilized against denaturation by a variety of environmental stresses as well as to chemical scission of their disulfide bonds and to hydrolysis by proteolytic enzymes (8,9j. Such a seemingly simple question as to why these iron complexes, as well as some other proteins, are much more stable than others is still impossible to answer with presently available information. 

Another variation that may affect the dynamic properties of different transferrins is in the number and distribution of disulfide bonds. Because conformational change is important for metal binding and release (Section V) the restraints imposed by these covalent bridges may be important. The likely distribution of disulfide bonds in different species is given in Table V. While these are deduced from sequence alignments and are thus tentative, several conclusions can be drawn. All species appear to have the same six conserved disulfide bonds in their N-lobe... 

Jing S, Trowbridge IS. 1987. Identification of the intermolecular disulfide bonds of the human transferrin receptor and its lipid-attachment site. EMBO J. 6 327-31... 

Early experiments showed that a transferrin-polycation complex transported bacterial DNA into cells [12]. Ions are taken up by cells as an iron-transferrin complex by receptor-mediated endocytosis. Protamine or poly-lysine ligated by disulfide bonds to transferring and mixed with a lu-ciferase-encoding plasmid may bind the DNA because of the cationic properties of the complex [12]. Subsequently, avian ery-throblasts and human K-562 cells were incubated with the transferrin-polycation peptide-DNA complex, and the complexes were recognized and transported into the cells by receptor-mediated endocytosis and taken up into endosome-Hke intracellular vesicles [12]. Treatment with chloroquine (an agent that affects the endosomal pH) enhanced the uptake considerably. In contrast to other transfection methods, the transfection of cells with transferrin-mediated endocytosis did not cause significant cell death, because of the physiologi-... 

Thevis, M. Ogorzalek Loo, R. R. Loo, J. A. Mass spectrometric characterization of transferrins and their fragments derived by reduction of disulfide bonds. 

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