title: Structural characterization and pH-induced conformational transition of full-length KcsA.
abstract: The bacterial K+ channel KcsA from Streptomyces lividans was analyzed by neutron and x-ray small-angle solution scattering. The C-terminally truncated version of KcsA, amenable to crystallographic studies, was compared with the full-length channel. Analyzing the scattering data in terms of radius of gyration reveals differences between both KcsA species of up to 13.2 A. Equally, the real-space distance distribution identifies a 40 to 50 A extension of full-length KcsA compared to its C-terminally truncated counterpart. We show that the x-ray and neutron scattering data are amenable for molecular shape reconstruction of full-length KcsA. The molecular envelopes calculated display an hourglass-shaped structure within the C-terminal intracellular domain. The C-terminus extends the membrane spanning region of KcsA by 54-70 A, with a central constriction 10-30 A wide. Solution scattering techniques were further employed to characterize the KcsA channel under acidic conditions favoring its open conformation. The full-length KcsA at pH 5.0 shows the characteristics of a dumbbell-shaped macromolecular structure, originating from dimerization of the tetrameric K+ channel. Since C-terminally truncated KcsA measured under the same low pH conditions remains tetrameric, oligomerization of full-length KcsA seems to proceed via structurally changed C-terminal domains. The determined maximum dimensions of the newly formed complex increase by 50-60%. Shape reconstruction of the pseudooctameric complex indicates the pH-induced conformational reorganization of the intracellular C-terminal domain.
authors.affiliation: University of Oxford, Department of Biochemistry, Laboratory of Molecular Biophysics, Oxford OX1 3QU, United Kingdom.
authors.forename: Jochen
authors.initials: J
authors.lastname: Zimmer
authors.forename: Declan A
authors.initials: DA
authors.lastname: Doyle
authors.forename: J Günter
authors.initials: JG
authors.lastname: Grossmann
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D001665:Binding Sites; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D008958:Models, Molecular; D033363:Neutron Diffraction; D015221:Potassium Channels / Q000737:chemistry* / Q000648:ultrastructure*; D011485:Protein Binding; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding
chemical_list: D001426:Bacterial Proteins; D015221:Potassium Channels; C107790:prokaryotic potassium channel