title: Functionally active t1-t1 interfaces revealed by the accessibility of intracellular thiolate groups in kv4 channels.
abstract: Gating of voltage-dependent K(+) channels involves movements of membrane-spanning regions that control the opening of the pore. Much less is known, however, about the contributions of large intracellular channel domains to the conformational changes that underlie gating. Here, we investigated the functional role of intracellular regions in Kv4 channels by probing relevant cysteines with thiol-specific reagents. We find that reagent application to the intracellular side of inside-out patches results in time-dependent irreversible inhibition of Kv4.1 and Kv4.3 currents. In the absence or presence of Kv4-specific auxiliary subunits, mutational and electrophysiological analyses showed that none of the 14 intracellular cysteines is essential for channel gating. C110, C131, and C132 in the intersubunit interface of the tetramerization domain (T1) are targets responsible for the irreversible inhibition by a methanethiosulfonate derivative (MTSET). This result is surprising because structural studies of Kv4-T1 crystals predicted protection of the targeted thiolate groups by constitutive high-affinity Zn(2+) coordination. Also, added Zn(2+) or a potent Zn(2+) chelator (TPEN) does not significantly modulate the accessibility of MTSET to C110, C131, or C132; and furthermore, when the three critical cysteines remained as possible targets, the MTSET modification rate of the activated state is approximately 200-fold faster than that of the resting state. Biochemical experiments confirmed the chemical modification of the intact alpha-subunit and the purified tetrameric T1 domain by MTS reagents. These results conclusively demonstrate that the T1--T1 interface of Kv4 channels is functionally active and dynamic, and that critical reactive thiolate groups in this interface may not be protected by Zn(2+) binding.
authors.affiliation: Department of Pathology, Anatomy, and Cell Biology, Jefferson Medical College of thomas Jefferson University, Philadelphia, PA 19107, USA.
authors.forename: Guangyu
authors.initials: G
authors.lastname: Wang
authors.forename: Mohammad
authors.initials: M
authors.lastname: Shahidullah
authors.forename: Carmen A
authors.initials: CA
authors.lastname: Rocha
authors.forename: Candace
authors.initials: C
authors.lastname: Strang
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Pfaffinger
authors.forename: Manuel
authors.initials: M
authors.lastname: Covarrubias
mesh_terms: D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D019281:Dimerization; D007424:Intracellular Fluid; D015640:Ion Channel Gating / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D051379:Mice; D009865:Oocytes / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated / Q000737:chemistry / Q000502:physiology*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D051381:Rats; D051672:Shal Potassium Channels; D013329:Structure-Activity Relationship; D013438:Sulfhydryl Compounds / Q000737:chemistry / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: C497022:Kcnd3 protein, mouse; C497023:Kcnd3 protein, rat; D024642:Potassium Channels, Voltage-Gated; D021122:Protein Subunits; D051672:Shal Potassium Channels; D013438:Sulfhydryl Compounds