, Volume 38, Issue 7, pp 993-1002
Date: 02 Jun 2009

Conformational rearrangements in the S6 domain and C-linker during gating in CNGA1 channels

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This work completes previous findings and, using cysteine scanning mutagenesis (CSM) and biochemical methods, provides detailed analysis of conformational changes of the S6 domain and C-linker during gating of CNGA1 channels. Specific residues between Phe375 and Val424 were mutated to a cysteine in the CNGA1 and CNGA1cys-free background and the effect of intracellular Cd2+ or cross-linkers of different length in the open and closed state was studied. In the closed state, Cd2+ ions inhibited mutant channels A406C and Q409C and the longer cross-linker reagent M-4-M inhibited mutant channels A406Ccys-free and Q409Ccys-free. Cd2+ ions inhibited mutant channels D413C and Y418C in the open state, both constructed in a CNGA1 and CNGA1cys-free background. Our results suggest that, in the closed state, residues from Phe375 to approximately Ala406 form a helical bundle with a three-dimensional (3D) structure similar to those of the KcsA; furthermore, in the open state, residues from Ser399 to Gln409 in homologous subunits move far apart, as expected from the gating in K+ channels; in contrast, residues from Asp413 to Tyr418 in homologous subunits become closer in the open state.