Recombinant production of human Aquaporin-1 to an exceptional high membrane density in Saccharomyces cerevisiae.
Bottom Line: Aquaporin-1 was found to constitute 8.5 percent of total membrane protein content after expression at 15°C in a yeast host over-producing the Gal4p transcriptional activator and growth in amino acid supplemented minimal medium.A detergent screen for solubilization revealed that CYMAL-5 was superior in solubilizing recombinant Aquaporin-1 and generated a monodisperse protein preparation.Recombinant Aquaporin-1 produced in S. cerevisiae was not N-glycosylated in contrast to the protein found in human erythrocytes.
Affiliation: Aquaporin A/S, Copenhagen, Denmark.
In the present paper we explored the capacity of yeast Saccharomyces cerevisiae as host for heterologous expression of human Aquaporin-1. Aquaporin-1 cDNA was expressed from a galactose inducible promoter situated on a plasmid with an adjustable copy number. Human Aquaporin-1 was C-terminally tagged with yeast enhanced GFP for quantification of functional expression, determination of sub-cellular localization, estimation of in vivo folding efficiency and establishment of a purification protocol. Aquaporin-1 was found to constitute 8.5 percent of total membrane protein content after expression at 15°C in a yeast host over-producing the Gal4p transcriptional activator and growth in amino acid supplemented minimal medium. In-gel fluorescence combined with western blotting showed that low accumulation of correctly folded recombinant Aquaporin-1 at 30°C was due to in vivo mal-folding. Reduction of the expression temperature to 15°C almost completely prevented Aquaporin-1 mal-folding. Bioimaging of live yeast cells revealed that recombinant Aquaporin-1 accumulated in the yeast plasma membrane. A detergent screen for solubilization revealed that CYMAL-5 was superior in solubilizing recombinant Aquaporin-1 and generated a monodisperse protein preparation. A single Ni-affinity chromatography step was used to obtain almost pure Aquaporin-1. Recombinant Aquaporin-1 produced in S. cerevisiae was not N-glycosylated in contrast to the protein found in human erythrocytes.
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Mentions: CYMAL-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 hAQP1-GFP-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. Very importantly 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.