Membrane topology of Kch, a putative K+ channel from Escherichia coli

We have mapped the topology of the C-terminal half of the putative potassium channel protein Kch in the inner membrane of Escherichia coli using PhoA fusions. Our results are consistent with the widely assumed six-transmembrane helix model for eukaryotic voltage-gated ion channels and place both ends of the proposed channel-lining P-segment on the periplasmic side of the inner membrane. The rather hydrophobic P-segment is found to translocate only slowly across the inner membrane and seems to be near a threshold for stop-transfer function.