The possible role of a disulphide bond in forming functional Kir2.1 potassium channels

The role of two cysteine residues - Cys122 and Cys154 - in the structure of the strong inward rectifier K+ channel, Kir2.1, has been investigated usin g site-directed mutagenesis and electrophysiology. Such cysteine residues a re conserved across the inward rectifier family and may be expected to form a crucial disulphide bond. Our experiments show that when the cysteines ar e absent, the protein is expressed, but the channels are not functional, su ggesting that the disulphide bond is essential for correct channel assembly . However, reducing agents applied extracellularly have little effect on cu rrent amplitude in wild-type, so that, once the channel is assembled correc tly in the membrane, the disulphide bonds are no longer essential for funct ion. Molecular modelling suggests that a disulphide bond is formed - this m ay be either an intra- or an inter-subunit.