Specificity and localization of the hepatitis B virus-associated protein kinase

Abstract

The nature of the protein kinase (PK) which phosphorylates the core protein of hepatitis B virus in vitro was studied. The PK copurified with the core particles during rate zonal centrifugation and gel chromatography. It showed the same size heterogeneity as the core particles, which consisted of a main fraction of 28-nm particles and a subfraction of 22- to 26-nm particles. DNA-containing heavy core particles with a density of 1.33 to 1.35 g/ml and less endogenous PK than did the light cores. The phosphorylation reaction had a rapid initial phase (several minutes) and a slow but long-lasting second phase (many hours). The PK had a high affinity for ATP (KM = 0.5 mumol/liter). Only few of the several hundred P21.9 subunits in one core particle were phosphorylated in vitro. The only amino acid which was phosphorylated in vitro was serine. The resistance of the introduced phospho group against alkaline phosphatase showed that the PK acceptor, and probably the enzyme itself, was located inside the core particle.

Products of the “X” Gene in Hepatitis B and Related Viruses

“…infected liver tissue (10)(11)(12)(13). Such particles possess core antigen reactivity (HBcAg, GSHcAg, WHcAg and DHBcAg), an associated protein kinase activity (14)(15)(16) . Tissue samples were homogenized in ice-cold phosphatebuffered saline and centrifuged to eliminate cell debris, as described (13).…”

Probable implication of mutations of the X open reading frame in the onset of fulminant hepatitis B

“…Among several mutational hot spots in the core protein, a serine-to-proline mutation of the third-to-last aa is noteworthy. Since this serine seems to be phosphorylated before virus maturation [Gerlich et al, 1982;Roossinck and Siddiqui, 19871, its replacement by pro-line might disrupt the phosphorylationrelated virus maturation, leading to the onset of fulminant disease.…”

Inhibition of protein kinase C phosphorylation of hepatitis B virus capsids inhibits virion formation and causes intracellular capsid accumulation

“…This domain contains six potential serine phosphorylation sites (five in genotype H), which are targets for cellular protein kinase(s) (PK). PK activity is found in HBV capsids from different origins (Albin and Robinson, 1980;Gerlich et al, 1982).…”