Efficient expression of aquaporin Z in Escherichia coli cell-free system using different fusion vectors

Aquaporin Z (AqpZ) is a typical orthodox aquaporin with 6 transmembrane domains and five connecting loops. In order to express this complex membrane protein efficiently, E. coli cell-free expression system was employed as an alternative to produce aquaporin Z. Using different fusion vectors containing AqpZ gene, the expression level of fusion proteins in cell-free system varied from 7.97 to 578.35 microg/ml, while 7.34 to 340.81 microg/ml for target protein (AqpZ). The free energy of mRNA secondary structure at translation initiation region (TIR) was predicted and demonstrated a positive relationship with the expression level of AqpZ in cell-free system. This is the first report of expressing water channel protein in E. coli cell-free system, which has become a highly promising tool for fast and efficient production of integral membrane proteins.