title: Calcium-dependent gating of MthK, a prokaryotic potassium channel.
abstract: MthK is a calcium-gated, inwardly rectifying, prokaryotic potassium channel. Although little functional information is available for MthK, its high-resolution structure is used as a model for eukaryotic Ca(2+)-dependent potassium channels. Here we characterize in detail the main gating characteristics of MthK at the single-channel level with special focus on the mechanism of Ca(2+) activation. MthK has two distinct gating modes: slow gating affected mainly by Ca(2+) and fast gating affected by voltage. Millimolar Ca(2+) increases MthK open probability over 100-fold by mainly increasing the frequency of channel opening while leaving the opening durations unchanged. The Ca(2+) dose-response curve displays an unusually high Hill coefficient (n = approximately 8), suggesting strong coupling between Ca(2+) binding and channel opening. Depolarization affects both the fast gate by dramatically reducing the fast flickers, and to a lesser extent, the slow gate, by increasing MthK open probability. We were able to capture the mechanistic features of MthK with a modified MWC model.
authors.affiliation: Department of Biochemistry and Membrane Biology, University of California, Davis, 95616, USA.
authors.forename: Brittany
authors.initials: B
authors.lastname: Zadek
authors.forename: Crina M
authors.initials: CM
authors.lastname: Nimigean
mesh_terms: D019843:Archaeal Proteins / Q000378:metabolism / Q000502:physiology*; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D017014:Methanobacterium / Q000378:metabolism / Q000502:physiology*; D015221:Potassium Channels / Q000378:metabolism / Q000502:physiology*
chemical_list: D019843:Archaeal Proteins; D015221:Potassium Channels; D002118:Calcium