Ed in detergentIn order to purify the buy Vasopressin hAQP1-GFP-8His fusion protein we performed a detergent screen using six 79831-76-8 detergents commonly used for membrane protein purification. Data in Figure 7 show that CYMAL-5 was the most efficient detergent for solubilization of recombinant hAQP1-GFP-8His closely followed by DDM.Solubilized recombinant hAQP1-GFP-8His is monodisperse and mainly exists as a tetramerA suitable detergent efficiently solubilizes the membrane protein of interest, gives a monodisperse protein preparation and maintains protein stability over a long period of time. To analyze for these quality criteria we examined the fusion protein 
by fluorescent size exclusion chromatography (FSEC) [43] of hAQP1GFP-8His solubilized in CYMAL-5 or DDM to analyze for monodispersity. Data in Figure 8 show that the two detergents gave rise to similar chromatograms; a prominent symmetrical peak eluting in a total volume of less than 2 ml indicating a monodisperse protein preparation [35]. The elution volume corresponds to a molecular weight of approximately 200 kDa and indicates that solubilized, recombinant hAQP1-GFP-8His mainly exists as a tetramer in both detergents. Presence of a minor symmetrical peak shows that hAQP1-GFP-8His oligomers with aHigh Level Human Aquaporin Production in YeastFigure 3. In-gel fluorescence and western bloting of yeast membranes. A, in-gel fluorescence of SDS-PAGE separated crude membranes isolated from yeast expressing the AQP1-GFP fusion for the times indicated at 15uC or 30uC. B, western blotting of the gels 15900046 shown in `A’ using an antiGFP-antibody. Folding efficiency at each time point and temperature was estimated as the ratio between the intensity of correctly folded hAQP-1GFP fusion and the sum of intensities for the correctly folded and mal-folded GFP-fusions. MFP, mal-folded protein; CFP, correctly folded protein. The data are from a representative experiment. doi:10.1371/journal.pone.0056431.gstoichiometry larger than four also exist. There is no sign of protein degradation as no free-GFP peak is visible.CYMAL-5 solubilized Aquaporin1 can be purified by Ni2+affinity purificationCYMAL-5 efficiently solubilized hAQP1-GFP-His8 and produced a monodisperse protein preparation mainly consisting of the native tetrameric structure. We therefore selected CYMAL-5 solubilized hAQP1-GFP-8His for purification by affinity chromatography. A chromatogram 
resulting from the purification procedure is shown in Figure 9A. Data from the purification protocol revealed that 86 of the CYMAL-5 solubilized hAQP1GFP-8His protein bound to the Ni2+-resin and 62 of the solubilized and bound material was eluted with 250 mM imidazole. The peak-fraction collected after elution with 250 mM imidazole was analyzed by SDS-PAGE separation using in-gel fluorescence and Coomassie staining, Figure 9B. As expected monomeric, dimeric, trimeric as well as tetrameric hAQP1-GFP-8His proteins were visible. The Coomassie staining furthermore showed that solubilization of the hAQP1-GFP-8His protein by CYMAL-5 followed by Ni-affinity chromatography resulted in highly pure human Aquaporin-1 protein. Veryimportantly only protein bands visualized by in-gel fluorescence were observed in the Coomassie stain. None of the slower migrating, non-fluorescent and mal-folded hAQP1-GFP-8His proteins observed in the western blot in Figure 3 were present in the purified sample.DiscussionThe present paper describes an expression system and expression conditions that produce a.Ed in detergentIn order to purify the hAQP1-GFP-8His fusion protein we performed a detergent screen using six detergents commonly used for membrane protein purification. Data in Figure 7 show that CYMAL-5 was the most efficient detergent for solubilization of recombinant hAQP1-GFP-8His closely followed by DDM.Solubilized recombinant hAQP1-GFP-8His is monodisperse and mainly exists as a tetramerA suitable detergent efficiently solubilizes the membrane protein of interest, gives a monodisperse protein preparation and maintains protein stability over a long period of time. To analyze for these quality criteria we examined the fusion protein by fluorescent size exclusion chromatography (FSEC) [43] of hAQP1GFP-8His solubilized in CYMAL-5 or DDM to analyze for monodispersity. Data in Figure 8 show that the two detergents gave rise to similar chromatograms; a prominent symmetrical peak eluting in a total volume of less than 2 ml indicating a monodisperse protein preparation [35]. The elution volume corresponds to a molecular weight of approximately 200 kDa and indicates that solubilized, recombinant hAQP1-GFP-8His mainly exists as a tetramer in both detergents. Presence of a minor symmetrical peak shows that hAQP1-GFP-8His oligomers with aHigh Level Human Aquaporin Production in YeastFigure 3. In-gel fluorescence and western bloting of yeast membranes. A, in-gel fluorescence of SDS-PAGE separated crude membranes isolated from yeast expressing the AQP1-GFP fusion for the times indicated at 15uC or 30uC. B, western blotting of the gels 15900046 shown in `A’ using an antiGFP-antibody. Folding efficiency at each time point and temperature was estimated as the ratio between the intensity of correctly folded hAQP-1GFP fusion and the sum of intensities for the correctly folded and mal-folded GFP-fusions. MFP, mal-folded protein; CFP, correctly folded protein. The data are from a representative experiment. doi:10.1371/journal.pone.0056431.gstoichiometry larger than four also exist. There is no sign of protein degradation as no free-GFP peak is visible.CYMAL-5 solubilized Aquaporin1 can be purified by Ni2+affinity purificationCYMAL-5 efficiently solubilized hAQP1-GFP-His8 and produced a monodisperse protein preparation mainly consisting of the native tetrameric structure. We therefore selected CYMAL-5 solubilized hAQP1-GFP-8His for purification by affinity chromatography. A chromatogram resulting from the purification procedure is shown in Figure 9A. Data from the purification protocol revealed that 86 of the CYMAL-5 solubilized hAQP1GFP-8His protein bound to the Ni2+-resin and 62 of the solubilized and bound material was eluted with 250 mM imidazole. The peak-fraction collected after elution with 250 mM imidazole was analyzed by SDS-PAGE separation using in-gel fluorescence and Coomassie staining, Figure 9B. As expected monomeric, dimeric, trimeric as well as tetrameric hAQP1-GFP-8His proteins were visible. The Coomassie staining furthermore showed that solubilization of the hAQP1-GFP-8His protein by CYMAL-5 followed by Ni-affinity chromatography resulted in highly pure human Aquaporin-1 protein. Veryimportantly only protein bands visualized by in-gel fluorescence were observed in the Coomassie stain. None of the slower migrating, non-fluorescent and mal-folded hAQP1-GFP-8His proteins observed in the western blot in Figure 3 were present in the purified sample.DiscussionThe present paper describes an expression system and expression conditions that produce a.
