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Abstract

Membrane proteins often exist in their native membranes at low abundance. Therefore, strong overexpression is needed to attain a high cellular concentration of the protein of interest. Crucial steps in the production of membrane-bound proteins are not restricted to transcription and translation but include the insertion into and the folding of the protein within the membrane. Although membrane protein insertion and folding follows general principles, differences in the mechanisms between the prokaryotic and the eukaryotic systems are evident. The insertion of a prokaryotic membrane protein is a co-translational process. The co-translational insertion of a protein into the membrane involves the signal recognition particle and its receptor. Posttranslational modifications should be considered when producing a recombinant protein. Almost all eukaryotic membrane proteins that have been detected in the plasma membrane are glycosylated. Glycosylation of a protein might be important for its function and/or required for its correct folding, for the assembly of subunits, and also as a signal to guide the protein to the proper subcellular location. High-level production of active eukaryotic membrane proteins in E. coli, the most widely used bacteria, is still a challenge. This heterologous expression system often results in low yield, or the proteins tend to form insoluble inclusion bodies with inactive protein.