Application of Amphipols for Structure–Functional Analysis of TRP Channels
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Amphipathic polymers (amphipols), such as A8-35 and SApol, are a new tool for stabilizing integral membrane proteins in detergent-free conditions for structural and functional studies. Transient receptor potential (TRP) ion channels function as tetrameric protein complexes in a diverse range of cellular processes including sensory transduction. Mammalian TRP channels share ~20 % sequence similarity and are categorized into six subfamilies: TRPC (canonical), TRPV (vanilloid), TRPA (ankyrin), TRPM (melastatin), TRPP (polycystin), and TRPML (mucolipin). Due to the inherent difficulties in purifying eukaryotic membrane proteins, structural studies of TRP channels have been limited. Recently, A8-35 was essential in resolving the molecular architecture of the nociceptor TRPA1 and led to the determination of a high-resolution structure of the thermosensitive TRPV1 channel by cryo-EM. Newly developed maltose-neopentyl glycol (MNG) detergents have also proven to be useful in stabilizing TRP channels for structural analysis. In this review, we will discuss the impacts of amphipols and MNG detergents on structural studies of TRP channels by cryo-EM. We will compare how A8-35 and MNG detergents interact with the hydrophobic transmembrane domains of TRP channels. In addition, we will discuss what these cryo-EM studies reveal on the importance of screening different types of surfactants toward determining high-resolution structures of TRP channels.
KeywordsCryo-EM Amphipols Detergent TRPA1 TRPV1 TRPV2
A poly(sodium acrylate)-based amphipol compromising 35 % of free carboxylates, 25 % of octyl chains, 40 % of isopropyl groups
Transient receptor potential ankyrin
Transient receptor potential vanilloid
We would like to thank Teresa Cvetkov for her contribution to this project. We are also very grateful to Jean-Luc Popot for providing us with amphipols and helpful discussions. This work was supported by the American Heart Association (NCRP Scientist Development Grant 11SDG5280029), the American Lung Association Biomedical Research Grant (RG-166985-N), and the National Institute of Health Grant (NIGMS 1R01GM103899-01A1).
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