Receptor Dramatically Alter Ion Channel Function
نویسندگان
چکیده
Site-directed mutagenesis was used to mutate aCys418 and (3Cys447 in the M4 domain of Torpedo califomica acetylcholine receptor expressed in Xenopus laevis oocytes. The M4 region is a transmembrane domain thought to be located at the lipid-protein interface. By whole-cell voltage clamp analysis, mutation of both a subunits to aTrp418 increased maximal channel activity approximately threefold, increased the desensitization rate compared with wild-type receptor, and shifted the EC50 for acetylcholine from 32 pM to 13 pM. Patch measurements of single-channel currents revealed that the aTrp418 increased channel open times -28-fold at 1 30C with no effect on channel conductance. All of our measured functional changes in the aTrp418 mutant are consistent with a simple kinetic model of the acetylcholine receptor in which only the channel closing rate is altered by the mutation. Our results show that changes in protein structure at the putative lipid-protein interface can dramatically affect receptor function.
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