Mapping of maurotoxin binding sites on hKv1.2, hKv1.3, and hIKCa1 channels.
Maurotoxin (MTX) is a potent blocker of human voltage-activated Kv1.2 and intermediate-conductance calcium-activated potassium channels, hIKCa1. Because its blocking affinity on both channels is similar, although the pore region of these channels show only few conserved amino acids, we aimed to characterize the binding sites of MTX in these channels. Investigating the pH(o) dependence of MTX block on current through hKv1.2 channels, we concluded that the block is less pH(o) - sensitive than for hIKCa1 channels. Using mutant cycle analysis and computer docking, we tried to identify the amino acids through which MTX binds to hKv1.2 and hIKCa1 channels. We report that MTX interacts with hKv1.2 mainly through six strong interactions. Lys(23) from MTX protrudes into the channel pore interacting with the GYGD motif, whereas Tyr(32) and Lys(7) interact with Val(381), Asp(363), and Glu(355), stabilizing the toxin onto the channel pore. Because only Val(381), Asp(363), and the GYGD motif are conserved in hIKCa1 channels, and the replacement of His(399) from hKv1.3 channels with a threonine makes this channel MTX-sensitive, we concluded that MTX binds to all three channels through the same amino acids. Glu(355), although important, is not essential in MTX recognition. A negatively charged amino acid in this position could better stabilize the toxin-channel interaction and could explain the pH(o) sensitivity of MTX block on current through hIKCa1 versus hKv1.2 channels.
Visan
Violeta
V
Department of Applied Physiology, University of Ulm, Albert-Einstein-Allee 11, D-89081 Ulm, Germany.
Fajloun
Ziad
Z
Sabatier
Jean-Marc
JM
Grissmer
Stephan
S
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D019556:COS Cells; D006801:Humans; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; D051663:Kv1.2 Potassium Channel; D051664:Kv1.3 Potassium Channel; D008969:Molecular Sequence Data; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D024681:Potassium Channels, Calcium-Activated; D024642:Potassium Channels, Voltage-Gated / Q000187:drug effects / Q000378:metabolism*; D012604:Scorpion Venoms / Q000494:pharmacology*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496969:KCNA2 protein, human; C496973:KCNA3 protein, human; C496923:KCNN4 protein, human; D051663:Kv1.2 Potassium Channel; D051664:Kv1.3 Potassium Channel; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; D024642:Potassium Channels, Voltage-Gated; D012604:Scorpion Venoms; C104498:maurotoxin