Amino Acid Properties of Trafficking Determinants in the Outer Pore-Forming Region of Kv1 Potassium Channels in Cell Lines.

Different classes of Kv1 potassium channels have different trafficking patterns despite having very similar amino acid sequences. Two amino acids responsible for these differences have been identified in the outer pore turret region of Kv1.1 and Kv1.4. Here we tested a series of substitutions at these two determinants on Kv1.4. All P506 substitutions tested resulted in a significant decrease in surface protein, total protein, and protein half-life, indicating that proline is required at 506 to stabilize protein conformation and increase trafficking to the cell surface. All K533 substitutions tested had no effect on total protein, suggesting that the lysine at 533 is not important for maintaining Kv1.4 protein conformation. However, a basic or long polar amino acid, such as K, R, or Q, at this position favored high surface protein and efficient trafficking of Kv1.4, whereas an acidic or short amino acid, such as D, E, S, L, N, or H, at this position induced partial high endoplasmic reticulum-retention. This intracellular retention was not due to protein misfolding. We propose that these four prolines and four lysines in a Kv1.4 homotetramer might provide a binding site for a putative endoplasmic reticulum-export molecule to ensure high cell surface protein expression of the channel.