Fig. 1.
Models for TRK structure and for chloride conduction. a Tetramer co-organized by proximation of M1D helices in four separate TRK monomers: cylinder and wire diagrams in green, gray, blue, and red (counterclockwise) depict the backbone structures as originally proposed by Durell and Guy [23]. Cylinders represent TM helices M1D (near center) and M2D, while the other TM helices: M1A−M2A, M1B−M2B, M1C−M2C progress ccw within each monomer. Magenta figures represent the four selectivity sequences comprising the K+ pathway, central to each monomer: a QTGLO, b DLGYS, c SAGFT, and d TVGLS, for Trk1p in Schizosaccharomyces pombe. Central blue ball indicates the proposed pathway for chloride transit through the supertetramer [68]. Coordinate map provided by Dr. HR Guy. Drawing via PyMOL (DeLano Scientific, & Schrödinger LLC, Portland, OR, USA). b Diagram of two energy barriers to chloride transit, in series through the membrane dielectric. Parameters to be fitted, under stationary-state conditions, are a1, b2, A=exp(Eα/RT), and B=exp(Eβ/RT)