Kang Hee Yong, Lee Seungkeun, Park Sung Gyoo, Yu Jaehoon, Kim Youngsoo, Jung Guhung
School of Biological Sciences, Seoul National University, Shillim-dong, Seoul 151-742, South Korea.
Biochem J. 2006 Sep 1;398(2):311-7. doi: 10.1042/BJ20060347.
Protein-protein interactions can be regulated by protein modifications such as phosphorylation. Some of the phosphorylation sites (Ser155, Ser162 and Ser170) of HBV (hepatitis B virus) Cp have been discovered and these sites are implicated in the regulation of viral genome encapsidation, capsid localization and nucleocapsid maturation. In the present report, the dimeric form of HBV Cp was phosphorylated by PKA (protein kinase A), but not by protein kinase C in vitro, and the phosphorylation of dimeric Cp facilitated HBV core assembly. Matrix-assisted laser-desorption ionization-time-of-flight analysis revealed that the HBV Cp was phosphorylated at Ser87 by PKA. This was further confirmed using a mutant HBV Cp with S87G mutation. The S87G mutation inhibited the phosphorylation and, as a result, the in vitro HBV core assembly was not facilitated by PKA. In addition, when either pCMV/FLAG-Core(WT) or pCMV/FLAG-Core(S87G) was transfected into HepG2 cells, few mutant Cps (S87G) assembled into capsids compared with the wild-type (WT) Cps, although the same level of total Cps was expressed in both cases. In conclusion, PKA facilitates HBV core assembly through phosphorylation of the HBV Cp at Ser87.
蛋白质-蛋白质相互作用可通过蛋白质修饰（如磷酸化）来调节。乙肝病毒（HBV）核心蛋白（Cp）的一些磷酸化位点（Ser155、Ser162和Ser170）已被发现，这些位点与病毒基因组包装、衣壳定位和核衣壳成熟的调节有关。在本报告中，HBV Cp的二聚体形式在体外被蛋白激酶A（PKA）磷酸化，但未被蛋白激酶C磷酸化，并且二聚体Cp的磷酸化促进了HBV核心组装。基质辅助激光解吸电离飞行时间分析表明，HBV Cp在Ser87处被PKA磷酸化。使用具有S87G突变的突变型HBV Cp进一步证实了这一点。S87G突变抑制了磷酸化，结果，PKA未促进体外HBV核心组装。此外，当将pCMV/FLAG-Core(WT)或pCMV/FLAG-Core(S87G)转染到HepG2细胞中时，与野生型（WT）Cp相比，很少有突变型Cp（S87G）组装成衣壳，尽管在两种情况下表达的总Cp水平相同。总之，PKA通过将HBV Cp的Ser87磷酸化来促进HBV核心组装。
