Membrane-spanning domain of bovine foamy virus transmembrane protein having cytotoxicity

Foamy viruses (FVs) have broad cellular tropism infecting vertebrates from fish to human being,which indicates that Env protein has a high capability for membrane fusion.Conservative features in all FV transmembrane (TM) proteins include a region of hydrophobic domain called membrane-spanning domain (MSD),which contains several stretches of hydrophobic amino acids.To investigate whether these features were associated with the cytotoxicity effect of TM on Escherichia coli,a series of mutants were constructed and expressed in the E.coli BL21 (DE3) using pET-32a (+) as expressing vector.The results showed that only TM3 without MSD was expressed in E.coli,whereas the other two containing full or part of the MSD (TM1 and TM2) could not be expressed.Furthermore,the bacterial amount and living bacteria analysis revealed that the cytotoxicity of TM was dependent on its MSD,especially on the stretches of hydrophobic amino acids.Western blotting analysis showed that TM3 protein was purified with affinity purification.