Takada S, Koike K
Department of Gene Research, Cancer Institute (JFCR), Tokyo, Japan.
Virology. 1994 Dec;205(2):503-10. doi: 10.1006/viro.1994.1671.
The X protein of hepatitis B virus is known to be a trans-activator of viral and cellular genes and to be a serine protease inhibitor as well. X protein has no DNA-binding activity, but is postulated to exert its trans-activation function by interacting with cellular proteins. To investigate interaction sites of X protein with cellular proteins, we carried out an immunoprecipitation inhibition assay using several different anti-X antibodies in the presence or absence of cellular proteins. Results elucidated three separate sites (aa 65-72, aa 105-115, and aa 131-142; U22, X1, and Z44 sites, respectively) of the X protein that cooperatively interacted with cellular proteins. Analyses with a series of mutant X proteins also supported the interactions at the U22, X1, and Z44 sites. Based on the CAT activity assay, the essential regions for the trans-activation function of X protein overlapped with these three interaction sites. Furthermore, these interaction sites also coincide with the structures necessary for the serine protease inhibitor activity. Thus, the trans-activation function and serine protease inhibitor activity of X protein may be exerted by interaction with cellular proteins through at least these three sites.
已知乙型肝炎病毒的X蛋白是病毒和细胞基因的反式激活因子，也是一种丝氨酸蛋白酶抑制剂。X蛋白没有DNA结合活性，但推测它通过与细胞蛋白相互作用来发挥其反式激活功能。为了研究X蛋白与细胞蛋白的相互作用位点，我们在有或没有细胞蛋白存在的情况下，使用几种不同的抗X抗体进行了免疫沉淀抑制试验。结果阐明了X蛋白与细胞蛋白协同相互作用的三个独立位点（分别为氨基酸65 - 72、氨基酸105 - 115和氨基酸131 - 142；U22、X1和Z44位点）。对一系列突变X蛋白的分析也支持了在U22、X1和Z44位点的相互作用。基于CAT活性测定，X蛋白反式激活功能的必需区域与这三个相互作用位点重叠。此外，这些相互作用位点也与丝氨酸蛋白酶抑制剂活性所需的结构一致。因此，X蛋白的反式激活功能和丝氨酸蛋白酶抑制剂活性可能至少通过这三个位点与细胞蛋白的相互作用来发挥。
