GFP-based membrane protein overexpression and purification in E. coli and S. cerevisiae Joy Kim Center for Biomembrane Research Department of Biochemistry and Biophysics Stockholm University Stockholm, Sweden
Soluble protein vs. membrane protein structures
Solubilization with suitable detergent Purification Crystallization Structure determination Homologs of a target protein Overexpression screening Overexpression optimization Detergent screening GFP-based
E. coli
In-gel fluorescence vs. Western Blotting IGF WB
Overexpression of eukaryotic membrane proteins in E. coli Differences in lipid compositions Post translational modifications Folding environments Alternative overexpression hosts Yeast (P. pastoris, S. cerevisiae) Insect and mammalian cells Cell-free system Easy genetic manipulations Well known genetics ER quality control system
TEV site GFPHisX8GFPHisX8 GAL1 GFPHisX8 TEF Initial tests In two different yeast strains, one with Pep4 deletion In two different promoters, one inducible and the other constitutive
Fluorescence of whole-cell lysates from 10 ml vs. 1L cultures
Comparison of the upscale expression in 2.5 L shaker flask vs. 15 L fermenter
Time course for the overexpression of MP-GFP fusions
Fluorescence of whole-cell lysates vs. membrane fractions
Fluorescence In gel band intensity Fluorescence in solution vs. in-gel fluorescence
Combination of Gal1, an inducible promoter/Pep4, a vacuolar protease deletion strain gave the overall best overexpression for majority of test membrane proteins. Overexpression screening of yeast MP-GFP fusions
Optimizing expression with chemical chaperones
N-terminal vs. C-terminal GFP tagging 1: Rer1-GFP 2: GFP-Rer1
Assessing the quality of MP-GFP fusions by subcellular localization ConfocalWide field
Assessing the quality of MP-GFP fusions by FSEC Newstead et al., 2007, PNAS 104: Aggregation MP-GFP fusion Free GFP
Purification of a nucleotide sugar transporter Newstead et al., 2007, PNAS 104: Detergent solubilized membranesPurified MP-GFPPurified MP
GFP-based overexpression and purification of eukaryotic membrane proteins in S. cerevisiae Drew et al., Nat. Protocol, in press
Overexpression screening Solubilization with suitable detergent Purification Crystallization Structure determination Overexpression optimization Detergent screening Homologs of a target protein GFP-based
Acknowledgements Jan Willem de Gier Gunnar von Heijne David Drew Simon Newstead So Iwata Center for Biomembrane Research Stockholm University Stockholm, Sweden Membrane Crystallography group Imperial College London, U. K.