Flexibility of the Kir6.2 inward rectifier K+ channel pore

Citation
G. Loussouarn et al., Flexibility of the Kir6.2 inward rectifier K+ channel pore, P NAS US, 98(7), 2001, pp. 4227-4232
Citations number
26
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
ISSN journal
0027-8424 → ACNP
Volume
98
Issue
7
Year of publication
2001
Pages
4227 - 4232
Database
ISI
SICI code
0027-8424(20010327)98:7<4227:FOTKIR>2.0.ZU;2-7
Abstract
Interactions of sulfhydryl reagents with introduced cysteines in the pore-t erming (Kir6.2) subunits of the K-ATP channel were examined. 2-Aminoethyl m ethanethiosulfonate (MTSEA(+)) failed to modify Cd2+-insensitive control-Ki r6.2 channels, but rapidly and irreversibly modified Kir6.2[L164C] (L164C) channels. Although a single Cd2+ ion is coordinated by L164C, four MTSEA(+) " hits " can occur, each sequentially reducing the single-channel current. A dimeric fusion of control-Kir6.2 and L164C subunits generates Cd2+-insen sitive channels, confirming that at least three cysteines are required for coordination, but MTSEA(+) modification of the dimer occurs in two hits. L1 64C channels were not modified by bromotrimethyl ammoniumbimane (qBBr(+)), even though qBBr(+) caused voltage-dependent block las opposed to modificat ion) that was comparable to that of MTSEA(+) or 3-(triethylammonium)propyl methanethiosulfonate (MTSPTrEA(+)), implying that qBBr(+) can also enter th e inner cavity but does not modify L164C residues. The Kir channel pore str ucture was modeled by homology with the KcsA crystal structure. A stable co nformation optimally places the four L164C side chains for coordination of a single Cd2+ ion. Modification of these cysteines by up to four MTSEA(+) ( or three MTSPTrEA(+), or two qBBr(+)) does not require widening of the cavi ty to accommodate the derivatives within it. However, like the KcsA crystal structure, the energy-minimized model shows a narrowing at the inner entra nce, and in the Kir6.2 model this narrowing excludes all ions. To allow ent ry of ions as large as MTSPTrEA(+) or qBBr(+), the entrance must widen to > 8 Angstrom, but this widening is readily accomplished by minimal M2 helix m otion and side-chain rearrangement.