NONSTRUCTURAL PROTEIN-3 OF HEPATITIS-C VIRUS INHIBITS PHOSPHORYLATIONMEDIATED BY CAMP-DEPENDENT PROTEIN-KINASE

Inspection of the amino acid sequence of the non-structural region of the hepatitis C virus (HCV) gene product reveals a sequence of 14 amin o acids, g-Gly-Arg-Thr-Gly-Arg-Gly-Arg-Gly-Ile-Tyr-Arg1500, located in the non-structural protein, NS3. This sequence is highly similar to t he inhibitory site of the heat stable inhibitor of cAMP-dependent prot ein kinase (PKA) and to the autophpsphorylation site in the hinge regi on of the PKA type II regulatory domain. A synthetic peptide that corr esponds to the HCV sequence above and a set of shorter analogues act a s competitive inhibitors of PKA. A 43.5-kDa fragment of NS3 that consi sts of residues 1189-1525 of the HCV polyprotein inhibits PKA in a sim ilar range to the investigated synthetic peptides. In contrast to the short peptides, which show competitive inhibition, HCV-polyprotein-(11 89-1525) influences PKA in a mixed-inhibition-type manner. A possible mechanism explaining these differences is the formation of complexes t hat consist of the protein substrate, the enzyme and the HCV-polyprote in-(1189-1525). Binding studies with PKA and the non-hydrolysable ATP analogue [C-14]fluorosulfonylbenzoyladenosine and [H-3]cAMP do not rev eal any influence of the short HCV-derived peptides or HCV-polyprotein -(1189-1525) upon the affinity of PKA for these nucleotides. The compl ex interactions of the NS3 fragments could influence one of the most i mportant signal pathways of the cell and, therefore, could possibly pr ovide new pathological mechanisms for HCV infections of liver.