Molecular Properties of Kcv, a Virus Encoded K+ Channel

Abstract

The miniature viral K⁺ channel Kcv represents the pore module of all K⁺ channels. A synthetic gene of Kcv with an elevated GC content compared to that of the wild-type gene was expressed heterologously in Pichia pastoris, and the purified protein was functionally reconstituted into liposomes. Biochemical assays reveal a remarkable cation selctive stability of the channel tetramer via SDS−PAGE. Only cations, which permeate Kcv, were able to protect the oligomer against disassembly into monomers at high temperatures. Electrophysiological characterization of the single Kcv channel reveals a saturating conductance (Λ_max) of 360 pS; the single-channel current−voltage relation was strongly rectifying with a negative slope conductance at extreme voltages. The channel was highly selective for K⁺ and was blocked by Ba²⁺ and in a side specific manner by Na⁺ and Cs⁺ also. The channel conducted Rb⁺, but as a consequence, the channel was shifted into a hyperactive state. We conclude that specific binding interactions of cations in the conductive pathway are an important determinant of channel stability and function.