Biochemical Characterization of Suramin as a Selective Inhibitor for the PKA-Mediated Phosphorylation of HBV Core Protein in Vitro

The inhibitory effect of suraminon the phosphorylationof GST-HBV core fusion protein (GST-Hcore) and two GST-Hcore fusion polypeptides (Hcore157B and Hcore164B) by two α-type cAMP-dependent protein kinases (PKAIα and PKAIIα) was biochemically investigated in vitro. It was found that (i) this phosphorylationwas inhibited by suraminat a low concentration ( IC50= approx. 10 nM); (ii) a relative high dose of suraminwas required to inhibit an autophosphorylationof PKAIIα ( IC50= approx. 0.7 μM) and the PKAIIα-mediated phosphorylationof histone H2B( IC50= approx. 0.4 μM); (iii) the PKAIIα-mediated phosphorylationof Hcore157B was more sensitive to suraminthan the phosphorylationof Hcore157B by Ca2+-dependent protein kinase (PKC); and (iv) suraminhad a high binding affinity for Hcore157B, but not for histone H2Bin vitro. These results suggest that suraminselectively inhibits the PKA-mediated phosphorylationof HBV-CP through the direct binding in vitro of suraminto the Arg-rich C-terminal region (containing three potential phosphorylationsites for PKA) on HBV-CP.