Competition between Slc7a5 and LMAN2 for modulation of Kv1.2 gating.

Abstract

The voltage-gated potassium channel Kv1.2 is a prominent ion channel in the CNS, where it regulates electrical activity. Kv1.2 structure and function are well understood, but its regulation by auxiliary proteins has not been widely studied. We identified novel regulators of Kv1.2 by a mass spectrometry approach, including the neutral amino acid transporter Slc7a5, which causes a dramatic hyperpolarizing shift of channel activation. In contrast, LMAN2 is a recently identified candidate regulator that has the opposite effect on gating: large depolarizing voltages are required to activate Kv1.2 channels co-expressed with LMAN2. In this study, we characterized the functional interaction between LMAN2 and Slc7a5 on Kv1.2 gating properties, and identified key structural elements that underlie sensitivity to either regulator. When LMAN2 and Slc7a5 are expressed together, Kv1.2 activation exhibits a bimodal voltage-dependence, suggesting two distinct populations of channels regulated either by LMAN2 or Slc7a5, but not both. Kv1.5 is a close homolog of Kv1.2, but insensitive to both LMAN2 and Slc7a5. Using a Kv1.2:1.5 chimeric approach, we identified the S1 segment of the voltage sensing domain (VSD) as essential for Slc7a5 sensitivity, and the S2-S3 linker of the VSD for LMAN2 sensitivity. By replacing either segment with sequence from Kv1.5, modulation by the corresponding regulator was selectively abolished. Replacement of the S1-S3 segment of Kv1.2 with sequence from Kv1.5 rendered the channel insensitive to both forms of regulation. These results suggest that Slc7a5 and LMAN2 compete for interaction with the Kv1.2 voltage sensor, leading to complex voltage-dependence of channel activity when both regulators are present in the cell. Although the structural basis for this modulation remains uncertain, Kv1.2 clearly exhibits a propensity for modulation over a wide range of voltages.