Urea unfolding of opsin in phospholipid bicelles

Craig Mckibbin, Craig McKibbin, Nicola A. Farmer, Patricia C. Edwards, Claudio Villa, Paula J. Booth

    Research output: Contribution to journalArticlepeer-review


    Opsin is the unstable apo-protein of the light-activated G protein-coupled receptor rhodopsin. We investigated the stability of bovine opsin, solubilized in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)/detergent bicelles, against urea-induced unfolding. A single irreversible protein unfolding transition was observed from changes in intrinsic tryptophan fluorescence and far-UV circular dichroism. This unfolding transition correlated with loss of protein activity. Changes in tertiary structure, as indicated by fluorescence measurements, were concomitant with an approximate 50% reduction in α-helical content of opsin, indicating that global unfolding had been induced by urea. The urea concentration at the midpoint of unfolding was dependent on the lipid/detergent environment, occurring at approximately 1.2 m urea in DMPC/1,2-dihexanoyl-sn-glycero-3-phosphocholine bicelles, while being significantly stabilized to approximately 3.5 m urea in DMPC/3- [(cholamidopropyl)dimethylammonio]-1-propanesulfonate bicelles. These findings demonstrate that interactions with the surrounding lipids and detergent are highly influential in the unfolding of membrane protein structure. The urea/bicelle system offers the possibility for a more detailed understanding of the structural changes that take place upon irreversible unfolding of opsin. © 2009 The Authors.
    Original languageEnglish
    Pages (from-to)494-500
    Number of pages6
    JournalPhotochemistry and Photobiology
    Issue number2
    Publication statusPublished - Mar 2009


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