I am trying to express in E. coli four different membrane proteins (ABC transporter) in either a pET vector with an N-terminal 6x his-tag or an pASK-IBA vector (tet promotor) with N- or C-terminal strep-tag, respectively. I tried different concentrations of inductor, different times of expression, different temperatures... Under all condition the proteins seem to be toxic (decrease in OD), and I cannot detect anything of the right size after fractionation and column purifcation or just fractionation western blotting, antibody detection.
Has anyone an idea how I can get my proteins?
Thanks for your advice!