Abstract
The voltage-gated K+ (Kv) channel subunit Kv6.4 does not form functional channels on its own but tetramerizes with Kv2.1 subunits into functional Kv2.1/Kv6.4 heterotetramers with a proposed 3:1 stoichiometry. Within these Kv2.1/Kv6.4 heterotetramers, Kv6.4 causes an approximately 40 mV hyperpolarizing shift in the voltage-dependence of inactivation as compared to Kv2.1 homotetramers without affecting the voltage-dependence of activation significantly. By comparing the gating current (IQ) recordings of homotetrameric Kv2.1 and heterotetrameric Kv2.1/Kv6.4 channels, we recently showed that a second component in the charge (Q) versus voltage (V) distribution appeared in heterotetramers. Since this component develops at more negative potentials than Kv2.1 homotetramers, these results suggest that the voltage sensor of Kv6.4 subunits move in a more negative voltage range than the remaining Kv2.1's voltage sensors. Using cysteine accessibility studies, we show here that the voltage dependence of the rates of MTSET modification at V335C in Kv6.4 correspond with the second component of the QV distribution of Kv2.1/Kv6.4 heterotetramers. Similarly, the voltage dependence of modification rates at V296C in Kv2.1 follow the QV distribution of Kv2.1 homotetramers. These results indicate that in functional Kv2.1/Kv6.4 heterotetramers voltage sensors from Kv6.4 subunits move at more negative potentials than voltage sensors belonging to Kv2.1 subunits. (Supported by a FWO postdoctoral fellowship and FWO travel grant to EB and the Intramural Section Program of the National Institute of Neurological Disorders and Stroke, National Institutes of Health to MH)
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