KCNQ1/KCNE1 assembly, co-translation not required

Area of Science:

• Molecular biology
• Ion channel biophysics
• Cellular physiology

Background:

• Voltage-gated potassium (K(V)) channels are modulated by accessory proteins like KCNE, enhancing functional diversity.
• The assembly mechanism of KCNE proteins with K(V) channels, particularly KCNQ1 with KCNE1 for the cardiac I(Ks) current, remains unclear.
• Previous studies suggest co-translational assembly for some K(V) channel-accessory protein complexes.

Purpose of the Study:

• To investigate the assembly process of KCNE1 accessory protein with KCNQ1 potassium channel subunits.
• To determine if KCNQ1 and KCNE1 assembly occurs co-translationally or post-translationally.
• To elucidate the trafficking pathway of functional KCNQ1-KCNE1 channels.

Main Methods:

• Heterologous expression of KCNQ1 in Xenopus oocytes.
• Modulation of KCNQ1 by purified recombinant KCNE1 (prKCNE1).
• Treatment with cycloheximide (protein synthesis inhibitor) and brefeldin A (ER-Golgi transport inhibitor).
• Assessment of channel function and trafficking using electrophysiology and mutated KCNE1 variants.

Main Results:

• Purified recombinant KCNE1 modulated KCNQ1 channels, generating the I(Ks) current.
• Cycloheximide treatment did not prevent I(Ks) expression after prKCNE1 injection, indicating non-co-translational assembly.
• Brefeldin A treatment inhibited KCNQ1 modulation by prKCNE1, suggesting assembly occurs early in the secretory pathway.
• A trafficking-deficient KCNE1 mutant (KCNE1-L51H) reduced KCNQ1 currents, highlighting the importance of proper trafficking.

Conclusions:

• KCNE1 assembly with KCNQ1 does not require co-translational processes.
• Functional KCNQ1-KCNE1 channels assemble early in the secretory pathway.
• Vesicular trafficking is essential for delivering functional KCNQ1-KCNE1 channels to the plasma membrane.