The Selectivity Filter
The atomic model for the K1 channel
selectivity filter was based on the experimental
electron density map, which
showed a continuous ridge of electron
density attributable to the main chain, as
well as strong Val and Tyr side chain
density directed away from the pore (Fig.
8A). We also used K1 ion positions defined
by difference Fourier analysis (Figs. 6
and 8A, yellow density) and our knowledge
of alkali metal cation coordination in
small molecules. The side chain locations
preclude their direct participation in ion
coordination, leaving this function to the