Interactions of aptamers with sera albumins

The interactions of two short aptamers to human and bovine serum albumins were studied by fluorescence spectroscopic techniques. Intrinsic fluorescence of BSA and HSA were measured by selectively exciting their tryptophan residues. Gradual quenching was observed by titration of both proteins with aptamers. Aptamers are oligonucleic acid or peptide molecules that bind a specific target and can be used for both biotechnological and clinical purposes, since they present molecular recognition properties like that commonly found in antibodies. Two aptamers previously selected against the MUC1 tumour marker were used in this study, one selected for the protein core and one for the glycosylated MUC1. Stern-Volmer graphs were plotted and quenching constants were estimated. Plots obtained from experiments carried out at 25 °C and 37 °C showed the quenching of fluorescence of by aptamers to be a collisional phenomenon. Stern-Volmer constants estimated for HSA quenched by aptamer A were 1.68 × 10(5) (± 5 × 10(3))M(-1) at 37 °C, and 1.37 × 10(5) (± 10(3))M(-1) at 25 °C; and quenched by aptamer B were 1.67 × 10(5) (± 5 × 10(3))M(-1) at 37 °C, and 1.32 × 10(5) (± 10(3))M(-1) at 25 °C. Results suggest that the primary binding site for aptamers on albumin is close to tryptophan residues in sub domain IIA.