Recognition of single- and double-stranded oligonucleotides by bovine serum albumin via nonspecific interactions.

The complexes formed by bovine serum albumin (BSA) with single-stranded oligonucleotide (ss-oligo) or double-stranded oligonucleotide (ds-oligo) were investigated by laser light scattering, zeta potential analysis, and atomic force microscopy. It was found that BSA was able to recognize ss-oligo and ds-oligo upon forming complexes in HCOOH-HCOONa buffer at pH 3.0. When oligonucleotide was added dropwise to BSA, BSA formed a complex with ss-oligo but not with ds-oligo in the studied charge ratio. When BSA was added to oligonucleotides, BSA formed complexes with both ss-oligo and ds-oligo but via different paths: the BSA/ds-oligo underwent two processes, heavy precipitation followed by reentry, with increasing BSA/oligo charge ratio, whereas BSA/ss-oligo underwent only aggregation process, but with a charge reversal occurred at BSA/oligo charge ratio about 0.1. Moreover, the complex formed by BSA and ds-oligo showed a kinetics much slower than that of BSA and ss-oligo. We attributed the big difference upon complexation to the physical nature of oligonucleotides as well as the conformational change of BSA under severe conditions. The differentiation of ss-oligo from ds-oligo by BSA via nonspecific interactions gained insight in the recognition of DNA or RNA by specific protein (enzyme) under physiological conditions.