Secondary structure formation of a transmembrane segment in Kv channels

Transmembrane segments in the intact voltage-gated potassium (Kv) channel are helical, To ascertain whether this helicity could first be manifested inside the ribosomal tunnel, we generated biogenic peptide intermediates of Kv1.3 and mass-tagged the cysteine-scanned S6 trans membrane segment using pegylation (PEG-MAL) and calmodulation (CaM-MAL). For reference. we created an extended peptide that was used as a molecular tape measure of the ribosornal tunnel and determined that the functional length of the tunnel is 99-112 angstrom. We demonstrate that the S6 segment forms a compact structure inside the ribosomal tunnel and that the N-terminal half of S6 compacts more than the C-terminal half of S6. These results bear on the earliest folding events during biogenesis of ion channels.