Identification of two oligodeoxyribonucleotide binding proteins on plasma membranes of human cell lines

Two oligodeoxyribonucleotide (oligodN) binding proteins of approximately 100-110 kDa were identified in the plasma membranes of human HL-60, HepG2, H1, and KB cells by a photolabeling technique. Solubilization of cellular membranes with a nonionic detergent did not interfere with the binding of these two proteins to oligodNs, and both proteins were susceptible to serine protease action. The binding affinities of these two proteins to oligodNs were found to be similar; Scatchard plot analysis revealed the Kd for phosphodiester (PO) 21-mer oligodeoxycytidine to be 60 nM and binding sites numbered approximately 1.2 x 10(6)/cell for HepG2 cells. Both phosphorothioate (PS) and PO oligodNs could bind to these two proteins with the binding affinity for PS oligodNs being much stronger than that for PO oligodNs. The binding to oligodNs was affected by the ionic strength of the reaction. Dextran sulfate, tRNA, and double-stranded DNA inhibited the binding of oligodNs, whereas ATP, ADP, AMP, and TTP had no effect. Given their high affinity for oligodNs, these membranes proteins may play an important role in the action of oligodNs.