title: A competing hydrophobic tug on L596 to the membrane core unlatches S4-S5 linker elbow from TRP helix and allows TRPV4 channel to open.
abstract: We have some generalized physical understanding of how ion channels interact with surrounding lipids but few detailed descriptions on how interactions of particular amino acids with contacting lipids may regulate gating. Here we discovered a structure-specific interaction between an amino acid and inner-leaflet lipid that governs the gating transformations of TRPV4 (transient receptor potential vanilloid type 4). Many cation channels use a S4-S5 linker to transmit stimuli to the gate. At the start of TRPV4's linker helix is leucine 596. A hydrogen bond between the indole of W733 of the TRP helix and the backbone oxygen of L596 secures the helix/linker contact, which acts as a latch maintaining channel closure. The modeled side chain of L596 interacts with the inner lipid leaflet near the polar-nonpolar interface in our model-an interaction that we explored by mutagenesis. We examined the outward currents of TRPV4-expressing Xenopus oocyte upon depolarizations as well as phenotypes of expressing yeast cells. Making this residue less hydrophobic (L596A/G/W/Q/K) reduces open probability [Po; loss-of-function (LOF)], likely due to altered interactions at the polar-nonpolar interface. L596I raises Po [gain-of-function (GOF)], apparently by placing its methyl group further inward and receiving stronger water repulsion. Molecular dynamics simulations showed that the distance between the levels of α-carbons of H-bonded residues L596 and W733 is shortened in the LOFs and lengthened in the GOFs, strengthening or weakening the linker/TRP helix latch, respectively. These results highlight that L596 lipid attraction counteracts the latch bond in a tug-of-war to tune the Po of TRPV4.
authors.affiliation: Laboratory of Molecular and Cell Biology, University of Wisconsin, Madison, WI 53706; Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390.
authors.forename: Jinfeng
authors.initials: J
authors.lastname: Teng
authors.affiliation: Laboratory of Molecular and Cell Biology, University of Wisconsin, Madison, WI 53706.
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Loukin
authors.affiliation: Department of Biology, University of Maryland, College Park, MD 20742.
authors.forename: Andriy
authors.initials: A
authors.lastname: Anishkin
authors.affiliation: Laboratory of Molecular and Cell Biology, University of Wisconsin, Madison, WI 53706; Department of Genetics, University of Wisconsin, Madison, WI 53706 ckung@wisc.edu.
authors.forename: Ching
authors.initials: C
authors.lastname: Kung
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D000073659:Gain of Function Mutation; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D015640:Ion Channel Gating / Q000187:drug effects; D008055:Lipids / Q000737:chemistry; D000073658:Loss of Function Mutation; D008566:Membranes / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D010641:Phenotype; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D013329:Structure-Activity Relationship; D050916:TRPV Cation Channels / Q000819:agonists / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014981:Xenopus; D015003:Yeasts / Q000235:genetics / Q000378:metabolism
chemical_list: D000596:Amino Acids; D008055:Lipids; D050916:TRPV Cation Channels
keywords: TRP channels; TRP domain; gating; lipids; opening mechanism