Tomohiro Makino and George Georgiou are with the Department of Chemical Engineering, The University of Texas at Austin and the Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712, USA -- George Gerorgiou is with the Department of Biomedical Engineering, The University of Texas at Austin and the Section of Molecular Genetics and Microbiology, The University of Texas at Austin, Austin, Texas 78712, USA -- Georgios Skretas is with the Insitute of Biological Research and Biotechnology, National Hellenic Research Foundation, 48 Vassileos Constantinou Ave., 11635 Athens, Greece -- Tomohiro Makino is with the Asubio Pharma CO., LTD. 6-4-3, Minatojima-Minamimachi Chuo-ku, Kobe 650-0047, JapanProtein expression in Escherichia coli represents the most facile approach for the preparation of non-glycosylated proteins for analytical and preparative purposes. So far, the optimization of recombinant expression has largely remained a matter of trial and error and has relied upon varying parameters, such as expression vector, media composition, growth temperature and chaperone co-expression. Recently several new approaches for the genome-scale engineering of E. coli to enhance recombinant protein expression have been developed. These methodologies now enable the generation of optimized E. coli expression strains in a manner analogous to metabolic engineering for the synthesis of low-molecular-weight compounds. In this review, we provide an overview of strain engineering approaches useful for enhancing the expression of hard-to-produce proteins, including heterologous membrane proteins.Chemical EngineeringInstitute for Cellular and Molecular BiologyBiomedical EngineeringMolecular [email protected]