Biophysical effects of pore mutations of ROMK1

Potassium channels are ubiquitous, being present in all living organisms. T hese proteins share common structural elements, which confer common functio nal features. In general, all K+ channels have a high selectivity for K+, a nd are blocked by cations of similar dimensions, such as Cs+ and Ba2+. Muta tions in the pore region tend to lead to either the total loss of function or K+ selectivity, We have made mutations to one of the most highly conserv ed residues of the pore, glycine-143, of the inward rectifier ROMKI (Kir1.1 ), and examined the resulting channel properties in the Xenopus oocyte expr ession system with a two-electrode voltage clamp. Mutations G143A and G143R resulted in failure to express functional channels. Co-injection of wild-t ype ROMKI cRNA with these mutants led to rescue of channel function, which was different from wi id-type ROMKI. In both mutants, the sensitivity to Ba 2+ and Cs+ was increased, the rate of onset of block by Ba2+ was enhanced, and the selectivity to potassium was reduced. Whereas the crystallographic evidence shows that cations bind to the carbonyl backbone of the pore-linin g residues, the present results indicate that the side chains of these amin o acids, which face away from the pore lining, also affect permeation.