K+ PORE STRUCTURE REVEALED BY RECEPTOR CYSTEINES AT INNER AND OUTER SURFACES

The structure of the carboxyl half of the pore-forming region of Kv2.1 was studied by replacing each of 15 consecutive residues between posi tions 383 and 369 with a reporter cysteine residue. Extracellular appl ication of charged, membrane-impermeant methanethiosulfonates irrevers ibly modified currents at four cysteine-substituted positions, K382, Y 380, I379, and D378. intracellular exposure to methanethiosulfonate et hyltrimethylammonium revealed another set of reactive mutants (V374, T 373, T372, and T370). Our results indicate that positions 378 and 374 are exposed at outer and inner mouths of the channel, respectively, an d immersed in the aqueous phase. In contrast to present topological mo dels, the 383-369 region appears to span the pore mainly as a nonperio dic structure.