Integral membrane proteins (IMPs) play diverse roles in cells ranging from transport to signal transduction but these proteins are seriously underrepresented in repositories of structural information such as the Protein Data Bank (PDB). Simple, reliable over-expression systems for the production of recombinant IMPs will relieve a serious bottleneck in structural biology efforts towards characterization of IMPs. To this end we have developed novel flow cytometric assays to quantitatively assess the amount of properly-folded recombinant IMP present in the membrane of the bacterium E. coli. Model E. coli IMPs as well as mammalian G-protein coupled receptors (GPCRs) are currently being studied using these flow cytometric assays. The effects of systematic depletion or over-expression of components of the signal recognition particle (SRP) pathway as well as several proteins implicated in membrane protein quality control on the expression of the model IMPs have been investigated and a novel effector of membrane protein biogenesis was identified. We are also currently using the flow cytometric assay combined with cell sorting to undertake genome-wide searches for additional positive effectors of IMP biogenesis.

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