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The prokaryotic potassium channel fromStreptomyces lividans, KcsA, is the first channel that has a known crystal structure of the transmembrane domain. The crystal structure of its soluble C-terminal domain, however, still remains elusive. | GCN4 enhances the stability of the pore domain of potassium channel KcsA Zhiguang Yuchi Victor P. T. Pau and Daniel S. C. Yang Department of Biochemistry and BiomedicalSciences Faculty of Health Sciences McMaster University Hamilton Canada Keywords GCN4 KcsA pore domain potassium channel tetramerization domain Correspondence D. S. C. Yang Department of Biochemistry and Biomedical Sciences Faculty of Health Sciences McMaster University 1200 Main Street West Hamilton ON L8N 3Z5 Canada Fax 1 905 522 9033 Tel 1 905 525 9140 E-mail yang@mcmaster.ca Received 9 September 2008 revised 6 October 2008 accepted 16 October 2008 doi 10.1111 j.1742-4658.2008.06747.x The prokaryotic potassium channel from Streptomyces lividans KcsA is the first channel that has a known crystal structure of the transmembrane domain. The crystal structure of its soluble C-terminal domain however still remains elusive. Biophysical and electrophysiological studies have previously implicated the essential roles of the C-terminal domain in pH sensing and in vivo channel assembly. We examined this functional assignment by replacing the C-terminal domain with an artificial tetramerization domain GCN4-LI. The expression of KcsA is completely abolished when its C-terminal domain is deleted but it can be rescued by fusion with GCN4-LI. The secondary and quaternary structures of the hybrid channel are very similar to those of the wild-type channel according to CD and gel-filtration analyses. The thermostability of the hybrid channel at pH 8 is similar to that of the wild-type but is insensitive to pH changes. This supports the notion that the pH sensor of KcsA is located in the C-terminal domain. The result obtained in the present study is in agreement with the proposed functions of the C-terminal domain and we show that the channel assembly role of the C-terminal domain can be substituted with a non-native tetrameric motif. Because tetramerization domains are found in different families of potassium .
