Two-dimensional crystallization and projection structure of KcsA potassium channel.
Potassium channels are integral membrane proteins that play a crucial role in regulating diverse cell functions in both electrically excitable and non-excitable cells. Molecular cloning has revealed a diverse family of genes that encode these proteins, and a variety of experimental strategies have defined functional domains. We have cloned, over-expressed and purified the KcsA potassium channel to homogeneity and reconstituted this channel protein with phospholipids to form two-dimensional crystals. The crystals belong to plane group p4 and have unit cell dimensions of a=b=48 A. A projection map at 6 A resolution has been obtained by electron crystallography. The map shows that the protein is a homotetramer, having a low-density region on the 4-fold axis that is the site of the ion conduction pathway. Each monomer contains density features that are consistent with the molecular model of a truncated form of KcsA recently determined by X-ray crystallography.
Li, HL; Sui, HX; Ghanshani, S; Lee, S; Walian, PJ; Wu, CL; Chandy, KG; Jap, BK
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