Abstract: A method is provided for producing a membrane protein folded to its native structure or active structure in a lipid disc or a liposome. The method comprises: (a) preparing a reaction solution for cell-free protein synthesis containing a polynucleotide encoding a membrane protein, a steroidal detergent, and a phospholipid, wherein the steroidal detergent is contained at a concentration higher than its critical micelle concentration; (b) decreasing the concentration of said steroidal detergent in the reaction solution; and (c) synthesizing the membrane protein simultaneously with formation of a lipid disk or liposome into which the synthesized membrane protein is integrated.

Abstract: A method is provided for producing a membrane protein folded to its native structure or active structure in a lipid disc or a liposome. The method comprises: (a) preparing a reaction solution for cell-free protein synthesis containing a polynucleotide encoding a membrane protein, a steroidal detergent, and a phospholipid, wherein the steroidal detergent is contained at a concentration higher than its critical micelle concentration; (b) decreasing the concentration of said steroidal detergent in the reaction solution; and (c) synthesizing the membrane protein simultaneously with formation of a lipid disk or liposome into which the synthesized membrane protein is integrated.

Abstract: We claim a method of expression a thioredoxin-fused membrane protein comprising expressing said thioredoxin-fused membrane protein in a cell-free protein synthesis system in the presence of a non-ionic detergent. It is preferable that the fused membrane protein which is a highly hydrophobic protein, e.g., a G protein-coupled receptor, can be produced in a state being highly soluble and capable of forming a biologically active three-dimensional structure. Also, this invention provides a recombinant polynucleotide encoding said thioredoxin-fused membrane protein which is expressed in the cell-free protein synthesis system.

Abstract: A fusion protein of thioredoxin with a target protein is expressed in a cell-free protein synthesis system to thereby synthesize at least a part of the fusion protein as a soluble protein. It is preferable that the target protein is a highly hydrophobic protein such as a membrane protein. In particular, a membrane protein such a G protein-coupled receptor can be produced in a state being highly soluble and capable of forming a biologically active three dimensional structure. Also, provided a recombinant vector for producing such a membrane protein in a cell-free protein synthesis system.