Bacterial K+ Channels - Lecture Notes PDF

Bacterial K+ Channels Structural Basis for Selectivity – Size-Gating 4 subunits, each with 2 TM helices and a third short helix that contribute to the pore → cone-shaped structure; 4 inner helices form the pore −vely charged amino acids present at the entrance to the channel responsible for specific...

Bacterial K+ Channels Structural Basis for Selectivity – Size-Gating 4 subunits, each with 2 TM helices and a third short helix that contribute to the pore → cone-shaped structure; 4 inner helices form the pore −vely charged amino acids present at the entrance to the channel responsible for specificity for +ve ions central channel with a constriction (selectivity filter) just large enough to allow K+ to pass through; K+ is 104 × faster than Na+ The K+ channel of Streptomyces lividans (KcsA) is the first ion channel structure solved by X-ray crystallography (1998) Bacterial K+ Channels Carbonyl oxygen atoms of peptide backbone interact with dehydrated K+, replacing interactions with H2O Fixed in rigid ring, optimal for K+ (1.32 Angstrom), cannot move inwards to coordinate with much smaller Na+ (0.95 Angstrom) 4 sites for K+ ions, but 2 of them are occupied by H2O molecules K+ ions move rapidly through the channel in single file by hopping between sites Selectivity filter is based on size so that K+ is preferentially stabilized (like valinomycin) The K+ ions repulse each other so that only two of the four sites are occupied at a given time. The effect of binding to carbonyl oxygens and repulsion between K+ ions makes sure that ions keep moving.