Measurement of interaction behavior of six biologically important noble metal ions with the iron(III) binding protein, apo-transferrin, using mobility-shift affinity electrophoresis

Transferrin is iron (III)-binding protein that transports Fe (III) ion to cells in different parts of the body. At saturation level 70% of transferrin remains free from iron (apo-transferrin), suggesting a broader scope of binding capabilities with non-iron (III) metal ions. Our previous work demonstrated that transferrin can effectively coordinate with noble metal ions. Hence to improve our understanding of the in-vitro metal-interaction behavior of the protein and how it correlates with its functions invivo, the interactions between apo-transferrin and medicinally important noble metals, Au (I), Au (III), Os (III), Pt (IV), Ir (III) and Ru (III) were investigated in the mobility shift mode of affinity capillary electrophoresis. The binding interactions were estimated according to the variation in electrophoretic mobility of the protein after coordination with the metal ions at physiological pH 7.4. Delta R/Rf values and confidence intervals were used to express the interaction results, which were calculated by using mobility ratios of protein with and without metal ions (R-f and R-i respectively) with respect to an electrophoretic marker (acetanilide). All the tested metal ions were found to be coordinated well with apo-transferrin, out of those Ir (III) exhibited the strongest interaction followed by the Au (I) ion. Noticeable variations in the shape and intensity of the protein peaks have been observed after interaction with some of the metal ions, especially those showing high binding affinities, which is probably due to conformational changes in the protein structure. The screening results suggest that apo-transferrin can interact with a variety of non-iron (III) metal ions and be the medium of transport for those metal ions into the biological system. This extended binding capability of apo-transferrin can be utilized for the targeted delivery of therapeutically significant metal ions. It can also be helpful in the development of new metal-based drugs for the treatment of a variety of ailments.