Enhanced functional expression of aquaporin Z via fusion of in situ cleavable leader peptides in Escherichia coli cell-free system

• Several leader peptides were fused to increase AqpZ expression in cell-free system.
• Leader peptide sequences could be in situ removed by adding detergents or liposome.
• The purified AqpZ from these cell-free systems was fully bioactive.

Aquaporin Z (AqpZ) is a water channel protein from Escherichia coli and has attracted many attentions to develop the biomimetic water filtration technology. Cell-free protein synthesis (CFPS) system, one of the most complex multi-enzymatic systems, has the ability of producing the integral membrane protein in vitro. To enhance the synthesis of AqpZ in E. coli cell-free system, several natural leader peptides were respectively fused at the N-terminus and were verified to enhance the expression level significantly. Moreover, the supplementation of detergents or liposome could activate leader peptidase from the cell-free extract and provide hydrophobic environment for proper folding of AqpZ. Thus, the release of mature AqpZ via the in situ removal of leader peptide was achieved, with a specific water transport activity of (2.1 ± 0.1) × 10−14 cm3 s−1 monomer−1. Using this in situ removable leader peptide strategy, the transcription–translation, leader sequence cleavage and membrane protein folding were integrated into a simple process in the cell-free system, providing a convenient approach to enhance the expression of target proteins, especially those membrane proteins difficult to achieve.