Role of the S2 and S3 segment in determining the activation kinetics in Kv2.1 channels.
We constructed chimeras between the rapidly activating Kv1.2 channel and the slowly activating Kv2.1 channel in order to study to what extent sequence differences within the S1-S4 region contribute to the difference in activation kinetics. The channels were expressed in Xenopus oocytes and the currents were measured with a two-microelectrode voltage-clamp technique. Substitution of the S1-S4 region of Kv2.1 subunits by the ones of Kv1.2 resulted in chimeric channels which activated more rapidly than Kv2.1. Furthermore, activation kinetics were nearly voltage-independent in contrast to the pronounced voltage-dependent activation kinetics of both parent channels. Systematic screening of the S1-S4 region by the replacement of smaller protein parts resolved that the main functional changes generated by the S1-S4 substitution were generated by the S2 and the S3 segment. However, the effects of these segments were different: The S3 substitution reduced the effective gating charge and accelerated both a voltage-dependent and a voltage-independent component of the activation time course. In contrast, the S2 substitution accelerated predominantly the voltage-dependent component of the activation time course thereby leaving the effective gating charge unchanged. It is concluded that the S2 and the S3 segment determine the activation kinetics in a specific manner.
Koopmann
R
R
Institut für Physiologie, Herz-Kreislauf-Physiologie, Friedrich-Schiller-Universität, 07740 Jena, Germany.
Scholle
A
A
Ludwig
J
J
Leicher
T
T
Zimmer
T
T
Pongs
O
O
Benndorf
K
K
D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D051668:Delayed Rectifier Potassium Channels; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000502:physiology; D007700:Kinetics; D051663:Kv1.2 Potassium Channel; D008845:Microinjections; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D016133:Polymerase Chain Reaction; D015221:Potassium Channels / Q000737:chemistry*; D024642:Potassium Channels, Voltage-Gated; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D051669:Shab Potassium Channels; D013329:Structure-Activity Relationship; D014982:Xenopus laevis
D051668:Delayed Rectifier Potassium Channels; C496969:KCNA2 protein, human; C496988:KCNB1 protein, human; C496972:Kcna2 protein, rat; C496991:Kcnb1 protein, rat; D051663:Kv1.2 Potassium Channel; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D011993:Recombinant Fusion Proteins; D051669:Shab Potassium Channels