Structural differences of bacterial and mammalian K+ channels.
Using a peptide toxin, kaliotoxin (KTX), we gained new insight into the topology of the pore region of a voltage-gated potassium channel, mKv1.1. In order to find new interactions between mKv1.1 and KTX, we investigated the pH dependence of KTX block which was stronger at pH(o) 6.2 compared with pH(o) 7.4. Using site-directed mutagenesis on the channel and the toxin, we found that protonation of His(34) in KTX caused the pH(o) dependence of KTX block. Glu(350) and Glu(353) in mKv1.1, which interact with His(34) in KTX, were calculated to be 4 and 7 A away from His(34)/KTX, respectively. Docking of KTX into a homology model of mKv1.1 based on the KcsA crystal structure using this and other known interactions as constraints showed structural differences between mKv1.1 and KcsA within the turret (amino acids 348-357). To satisfy our data, we would have to modify the KcsA crystal structure for the mKv1.1 channel orienting Glu(350) 7 A and Glu(353) 4 A more toward the center of the pore compared with KcsA. This would place Glu(350) 15 A and Glu(353) 11 A away from the center of the pore instead of the distances for the equivalent KcsA residues with 22 A for Gly(53) and 15 A for Gly(56), respectively. Bacterial and mammalian potassium channels may have structural differences regarding the turret of the outer pore vestibule. This topological difference between both channel types may have substantial influence on structure-guided development of new drugs for mammalian potassium channels by rational drug design.
Wrisch
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Department of Applied Physiology, University of Ulm, Albert-Einstein-Allee 11, 89081 Ulm, Germany.
Grissmer
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D000595:Amino Acid Sequence; D000818:Animals; D001419:Bacteria / Q000737:chemistry*; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D018698:Glutamic Acid / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D051662:Kv1.1 Potassium Channel; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010957:Plasmids / Q000378:metabolism; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated; D011485:Protein Binding; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry; D012604:Scorpion Venoms / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013816:Thermodynamics; D014407:Tumor Cells, Cultured
D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011994:Recombinant Proteins; D012604:Scorpion Venoms; C072276:kaliotoxin; D051662:Kv1.1 Potassium Channel; D018698:Glutamic Acid