Architecture of a K+ channel inner pore revealed by stoichiometric covalent modification.
Inwardly rectifying K+ channels bind intracellular magnesium and polyamines to generate inward rectification. We have examined the architecture of the inner pore of Kir2.1 channels by covalently attaching a constrained number (from one to four) of positively charged moieties of different sizes to the channel. Our results indicate that the inner pore is formed solely by the second transmembrane segment and is unprecedentedly wide. At a position critical for inward rectification (D172), the pore is sufficiently wide to bind three Mg2+ ions or polyamine molecules simultaneously. Single-channel recordings directly demonstrate that partially modified channels exhibit distinct subconductance levels. Such a wide inner pore may greatly facilitate ion permeation and high-affinity binding of multiple pore blockers to generate strong inward rectification.
Lu
T
T
Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
Nguyen
B
B
Zhang
X
X
Yang
J
J
D000595:Amino Acid Sequence; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003545:Cysteine / Q000737:chemistry / Q000235:genetics; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D008698:Mesylates / Q000737:chemistry; D008969:Molecular Sequence Data; D009154:Mutation; D009865:Oocytes; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure*; D024661:Potassium Channels, Inwardly Rectifying; D013439:Sulfhydryl Reagents / Q000737:chemistry; D014982:Xenopus laevis
D008698:Mesylates; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D013439:Sulfhydryl Reagents; D003545:Cysteine