Functional properties of KcsA R64 mutants

Abstract

The structural and functional properties of the potassium channel KcsA from the bacterium Streptomyces lividans are known to be influenced by lipids in various ways. Residue R64 in KcsA is implicated to be part of the lipid binding pocket and is involved in tetramer stability (chapter 4). In this study we investigated whether R64 is also involved in channel functioning. For this purpose we analyzed the channel conductance of two KcsA mutants (KcsA-R64D and KcsA-R64A) which were reconstituted into giant asolectin vesicles. It was found that both mutants had a similar conductance as KcsA-WT including the ability for high and low open probability gating. However both mutant channels were found to be less stable compared to KcsA-WT: the majority of KcsA-WT channels gate during periods of time up to hours, whereas a large number of mutant channels deactivates shortly after stimulation. This indicates that R64 plays a role in conformational rearrangements that are necessary for channel gating. Together the results suggest that gating and tetramer stability are linked, and that lipid binding to R64 is an key feature for both.