title: Drosophila photoreceptor cells exploited for the production of eukaryotic membrane proteins: receptors, transporters and channels.
abstract: BACKGROUND
  Membrane proteins (MPs) play key roles in signal transduction. However, understanding their function at a molecular level is mostly hampered by the lack of protein in suitable amount and quality. Despite impressive developments in the expression of prokaryotic MPs, eukaryotic MP production has lagged behind and there is a need for new expression strategies. In a pilot study, we produced a Drosophila glutamate receptor specifically in the eyes of transgenic flies, exploiting the naturally abundant membrane stacks in the photoreceptor cells (PRCs). Now we address the question whether the PRCs also process different classes of medically relevant target MPs which were so far notoriously difficult to handle with conventional expression strategies.
  
  
  RESULTS
  We describe the homologous and heterologous expression of 10 different targets from the three major MP classes--G protein-coupled receptors (GPCRs), transporters and channels in Drosophila eyes. PRCs offered an extraordinary capacity to produce, fold and accommodate massive amounts of MPs. The expression of some MPs reached similar levels as the endogenous rhodopsin, indicating that the PRC membranes were almost unsaturable. Expression of endogenous rhodopsin was not affected by the target MPs and both could coexist in the membrane stacks. Heterologous expression levels reached about 270 to 500 pmol/mg total MP, resulting in 0.2-0.4 mg purified target MP from 1 g of fly heads. The metabotropic glutamate receptor and human serotonin transporter--both involved in synaptic transmission--showed native pharmacological characteristics and could be purified to homogeneity as a prerequisite for further studies.
  
  
  CONCLUSIONS
  We demonstrate expression in Drosophila PRCs as an efficient and inexpensive tool for the large scale production of functional eukaryotic MPs. The fly eye system offers a number of advantages over conventional expression systems and paves the way for in-depth analyses of eukaryotic MPs that have so far not been accessible to biochemical and biophysical studies.
authors.affiliation: Department of Structural Biology, Heidelberg University Biochemistry Center (BZH), Heidelberg, Germany.
authors.forename: Valérie
authors.initials: V
authors.lastname: Panneels
authors.forename: Ines
authors.initials: I
authors.lastname: Kock
authors.forename: Jacomine
authors.initials: J
authors.lastname: Krijnse-Locker
authors.forename: Meriem
authors.initials: M
authors.lastname: Rezgaoui
authors.forename: Irmgard
authors.initials: I
authors.lastname: Sinning
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D004331:Drosophila melanogaster / Q000378:metabolism*; D005057:Eukaryotic Cells / Q000378:metabolism*; D015870:Gene Expression; D055785:Gene Knockdown Techniques; D006801:Humans; D007473:Ion Channels / Q000096:biosynthesis* / Q000302:isolation & purification; D026901:Membrane Transport Proteins / Q000096:biosynthesis* / Q000302:isolation & purification; D018377:Neurotransmitter Agents / Q000378:metabolism; D017956:Photoreceptor Cells, Invertebrate / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000096:biosynthesis* / Q000302:isolation & purification; D017470:Receptors, Glutamate / Q000378:metabolism; D011994:Recombinant Proteins / Q000302:isolation & purification; D012243:Rhodopsin / Q000378:metabolism
chemical_list: D007473:Ion Channels; D026901:Membrane Transport Proteins; D018377:Neurotransmitter Agents; D011956:Receptors, Cell Surface; D017470:Receptors, Glutamate; D011994:Recombinant Proteins; D012243:Rhodopsin