Polymer-Mediated Synthesis and Incorporation of Membrane Protein in Phospholipid Vesicles

Membrane proteins are involved in major cellular activities and are attractive pharmacological targets. Detergents are often required to extract membrane proteins from natural sources and keep them solubilized during purification and characterization. However, switching the environment from native membranes to detergents may also jeopardize structure and function of proteins. Here, we devised an alternative strategy for in vitro synthesizing membrane proteins in structurally and functionally relevant conformations by using synthetic polymers. Specifically, adding the polymer into cell-free protein synthesis system enabled direct synthesis of a peptide transporter PepTso and a water channel protein Aquaporin Z without the need of detergents or modification to proteins. Protein synthesis in the presence of both liposomes and the polymer resulted in the incorporation of proteins into phospholipid bilayers, which allowed proteins to transport oligopeptides and waters across liposome membrane respectively. Notably, the results suggest our initial assumption that the polymer can serve as a synthetic chaperone that sequesters the membrane proteins from water and still retains their structures and functionalities.