HBx, a transcriptional transactivating protein of hepatitis B virus (HBV), is required for viral infection and has been implicated in virus-mediated liver oncogenesis. However, the molecular mechanism for its influence on cell remains largely unknown. It was proved that HBx need the help of host cell proteins to exert its function by binding to them. During purifying of GSTX (fusion protein of GST and HBx) expressed in E. coli, we found that it can bind specifically with GrpE (HSP60) and DnaK (HSP70) of E. coli while GST cannot. Using GST pull-down, two-dimensional gel electrophoresis and mass spectrum, we found that GSTX can also bind to human mitochondrial HSP60 and HSP70, which are homologues of GrpE and DnaK. These interactions between HBx and mitochondrial HSP60 and HSP70 are supported by the result of co-immunoprecipitation experiment. It means that HBx can form complex with E. coli and human HSP60 and HSP70. The implication of HBx, HSP60 and HSP70 complex in molecular mechanism of virus infection is discussed.

The YWK-II component of human sperm membrane is related to the betaA4-amyloid precursor protein (APP) of Alzheimer's disease. A yeast 2-hybrid system was used to screen a mouse testis cDNA expression library for potential ligands capable of interacting with the extracellular domain of the YWK-II component. One of the bound proteins was identified as hDIA1, which has 96% identity with p140mDia. These proteins are members of the formin homology family and participate in cytokinesis and organization of the actin cytoskeleton. By interacting with these diaphanous proteins, the YWK-II component may be involved in germ cell differentiation and in the structural formation of the acrosome.