Conformational Dynamics in the Selectivity Filter of KcsA in Response to Potassium Ion Concentration

• Published in: Journal of molecular biology 2010-08, Vol.401 (2), p.155-166
• Main Authors: Bhate, Manasi P., Wylie, Benjamin J., Tian, Lin, McDermott, Ann E.
• Format: Article
• Language: English
• Subjects: Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Binding Sites; conformational dynamics; KcsA; Kinetics; Models, Molecular; Molecular Dynamics Simulation; Nuclear Magnetic Resonance, Biomolecular; Potassium - metabolism; potassium channel; Potassium Channels - chemistry; Potassium Channels - genetics; Potassium Channels - metabolism; Protein Conformation; Recombinant Proteins - chemistry; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; selectivity filter; solid-state NMR; Spectrum Analysis; Streptomyces lividans - genetics; Streptomyces lividans - metabolism; Water - chemistry
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/j.jmb.2010.06.031

Conformational change in the selectivity filter of KcsA as a function of ambient potassium concentration is studied with solid-state NMR. This highly conserved region of the protein is known to chelate potassium ions selectively. We report solid-state NMR chemical shift fingerprints of two distinct conformations of the selectivity filter; significant changes are observed in the chemical shifts of key residues in the filter as the potassium ion concentration is changed from 50 mM to 1 μM. Potassium ion titration studies reveal that the site-specific Kd for K+ binding at the key pore residue Val76 is on the order of ∼7 μM and that a relatively high sample hydration is necessary to observe the low-K+ conformer. Simultaneous detection of both conformers at low ambient potassium concentration suggests that the high-K+ and low-K+ states are in slow exchange on the NMR timescale (kex