title: Stereospecific binding of a disordered peptide segment mediates BK channel inactivation.
abstract: A number of functionally important actions of proteins are mediated by short, intrinsically disordered peptide segments, but the molecular interactions that allow disordered domains to mediate their effects remain a topic of active investigation. Many K+ channel proteins, after initial channel opening, show a time-dependent reduction in current flux, termed 'inactivation', which involves movement of mobile cytosolic peptide segments (approximately 20-30 residues) into a position that physically occludes ion permeation. Peptide segments that produce inactivation show little amino-acid identity and tolerate appreciable mutational substitutions without disrupting the inactivation process. Solution nuclear magnetic resonance of several isolated inactivation domains reveals substantial conformational heterogeneity with only minimal tendency to ordered structures. Channel inactivation mechanisms may therefore help us to decipher how intrinsically disordered regions mediate functional effects. Whereas many aspects of inactivation of voltage-dependent K+ channels (Kv) can be described by a simple one-step occlusion mechanism, inactivation of the voltage-dependent large-conductance Ca2+-gated K+ (BK) channel mediated by peptide segments of auxiliary β-subunits involves two distinguishable kinetic steps. Here we show that two-step inactivation mediated by an intrinsically disordered BK β-subunit peptide involves a stereospecific binding interaction that precedes blockade. In contrast, blocking mediated by a Shaker Kv inactivation peptide is consistent with direct, simple occlusion by a hydrophobic segment without substantial steric requirement. The results indicate that two distinct types of molecular interaction between disordered peptide segments and their binding sites produce qualitatively similar functions.
authors.affiliation: Department of Anesthesiology, Washington University School of Medicine, St Louis, Missouri 63110, USA.
authors.forename: Vivian
authors.initials: V
authors.lastname: Gonzalez-Perez
authors.forename: Xu-Hui
authors.initials: XH
authors.lastname: Zeng
authors.forename: Katie
authors.initials: K
authors.lastname: Henzler-Wildman
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Lingle
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects*; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D009865:Oocytes / Q000378:metabolism; D010455:Peptides / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism; D011485:Protein Binding; D021122:Protein Subunits / Q000037:antagonists & inhibitors / Q000378:metabolism; D051637:Shaker Superfamily of Potassium Channels / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D000596:Amino Acids; D051036:Large-Conductance Calcium-Activated Potassium Channels; D010455:Peptides; D021122:Protein Subunits; D051637:Shaker Superfamily of Potassium Channels; D011188:Potassium