title: Conformational flexibility in the binding surface of the potassium channel blocker ShK.
abstract: ShK is a 35-residue peptide that binds with high affinity to human voltage-gated potassium channels through a conserved K-Y dyad. Here we have employed NMR measurements of backbone-amide (15)N spin-relaxation rates to investigate motions of the ShK backbone. Although ShK is rigid on the ps to ns timescale, increased linewidths observed for 11 backbone-amide (15)N resonances identify chemical or conformational exchange contributions to the spin relaxation. Relaxation dispersion profiles indicate that exchange between major and minor conformers occurs on the sub-millisecond timescale. Affected residues are mostly clustered around the central helix-kink-helix structure and the critical K22-Y23 motif. We suggest that the less structured minor conformer increases the exposure of Y23, known to contribute to binding affinity and selectivity, thereby facilitating its interaction with potassium channels. These findings have potential implications for the design of new channel blockers based on ShK.
authors.affiliation: Department of Chemistry, Bar Ilan University, Ramat Gan 52900 (Israel).
authors.forename: Inbal
authors.initials: I
authors.lastname: Sher
authors.forename: Shih Chieh
authors.initials: SC
authors.lastname: Chang
authors.forename: Ying
authors.initials: Y
authors.lastname: Li
authors.forename: Sandeep
authors.initials: S
authors.lastname: Chhabra
authors.forename: Arthur G
authors.initials: AG
authors.lastname: Palmer
authors.forename: Raymond S
authors.initials: RS
authors.lastname: Norton
authors.forename: Jordan H
authors.initials: JH
authors.lastname: Chill
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008969:Molecular Sequence Data; D009587:Nitrogen Isotopes / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000737:chemistry* / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated / Q000037:antagonists & inhibitors* / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D009587:Nitrogen Isotopes; D010455:Peptides; D026902:Potassium Channel Blockers; D024642:Potassium Channels, Voltage-Gated
keywords: NMR spectroscopy; potassium channel blockers; protein dynamics; relaxation dispersion; structural biology