The topogenic function of S4 promotes membrane insertion of the voltage-sensor domain in the KvAP channel.
Voltage-dependent K+(KV) channels control K+permeability in response to shifts in the membrane potential. Voltage sensing in KVchannels is mediated by the positively charged transmembrane domain S4. The best-characterized KVchannel, KvAP, lacks the distinct hydrophilic region corresponding to the S3-S4 extracellular loop that is found in other K+channels. In the present study, we evaluated the topogenic properties of the transmembrane regions within the voltage-sensing domain in KvAP. S3 had low membrane insertion activity, whereas S4 possessed a unique type-I signal anchor (SA-I) function, which enabled it to insert into the membrane by itself. S4 was also found to function as a stop-transfer signal for retention in the membrane. The length and structural nature of the extracellular S3-S4 loop affected the membrane insertion of S3 and S4, suggesting that S3 membrane insertion was dependent on S4. Replacement of charged residues within the transmembrane regions with residues of opposite charge revealed that Asp72in S2 and Glu93in S3 contributed to membrane insertion of S3 and S4, and increased the stability of S4 in the membrane. These results indicate that the SA-I function of S4, unique among K+channels studied to date, promotes the insertion of S3 into the membrane, and that the charged residues essential for voltage sensing contribute to the membrane-insertion of the voltage sensor domain in KvAP.
Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aobayama 6-6-07, Sendai 980-8579, Japan.
Eriko
E
Mishima
Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aobayama 6-6-07, Sendai 980-8579, Japan.
Yoko
Y
Sato
Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aobayama 6-6-07, Sendai 980-8579, Japan.
Kei
K
Nanatani
Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aobayama 6-6-07, Sendai 980-8579, Japan.
Naomi
N
Hoshi
Department of Cardiovascular Regenerative Medicine, Graduate School of Medicine, Osaka University, 2-2 Yamada-oka, Suita 565-0871, Japan.
Jong-Kook
JK
Lee
Department of Biochemistry and Biophysics and Science for Life Laboratory, Stockholm University, Stockholm, Sweden.
Nina
N
Schiller
Department of Biochemistry and Biophysics and Science for Life Laboratory, Stockholm University, Stockholm, Sweden.
Gunnar
G
von Heijne
Graduate School of Life Science, University of Hyogo, Ako Hyogo 678-1297, Japan.
Masao
M
Sakaguchi
Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aobayama 6-6-07, Sendai 980-8579, Japan.
Nobuyuki
N
Uozumi
D000818:Animals; D004285:Dogs; D008954:Models, Biological; D010957:Plasmids / Q000235:genetics; D024642:Potassium Channels, Voltage-Gated / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000072417:Protein Domains / Q000235:genetics / Q000502:physiology; D021381:Protein Transport / Q000235:genetics / Q000502:physiology; D011817:Rabbits
D024642:Potassium Channels, Voltage-Gated
membrane structure; potassium channel; transmembrane domain; voltage-sensor