ID   KV53_BUNCI              Reviewed;          50 AA.
AC   C0HJC4;
DT   16-OCT-2013, integrated into UniProtKB/Swiss-Prot.
DT   16-OCT-2013, sequence version 1.
DT   25-MAY-2022, entry version 16.
DE   RecName: Full=Kappa-actitoxin-Bcs4a {ECO:0000305};
DE            Short=Kappa-AITX-Bcs4a {ECO:0000305};
DE   AltName: Full=Potassium channel toxin BcsTx3 {ECO:0000303|PubMed:23895459};
OS   Bunodosoma caissarum (Sea anemone).
OC   Eukaryota; Metazoa; Cnidaria; Anthozoa; Hexacorallia; Actiniaria;
OC   Actiniidae; Bunodosoma.
OX   NCBI_TaxID=31165;
RN   [1]
RP   PROTEIN SEQUENCE, FUNCTION, SUBCELLULAR LOCATION, AND MASS SPECTROMETRY.
RX   PubMed=23895459; DOI=10.1111/febs.12456;
RA   Orts D.J., Moran Y., Cologna C.T., Peigneur S., Madio B., Praher D.,
RA   Quinton L., De Pauw E., Bicudo J.E., Tytgat J., de Freitas J.C.;
RT   "BcsTx3 is a founder of a novel sea anemone toxin family of potassium
RT   channel blocker.";
RL   FEBS J. 280:4839-4852(2013).
CC   -!- FUNCTION: Inhibits voltage-gated potassium channels (Kv1/KCNA)
CC       (PubMed:23895459). Is potent on Drosophila Shaker IR channels
CC       (IC(50)=94.25 nM), and rKv1.2/KCNA2 (IC(50)=172.59 nM), and moderately
CC       active on hKv1.3/KCNA3 (IC(50)=1006.48 nM), rKv1.6/KCNA6
CC       (IC(50)=2245.93 nM), and Kv1.1/KCNA1 (IC(50) around 3 uM)
CC       (PubMed:23895459). In vivo, induces a rapid increase in swimming speed
CC       on zebrafish larvae, as well as death which occurs between 2 and 18
CC       hours later (By similarity). Also paralyzes swimming crabs (C.danae)
CC       when injected at the junction between the body and the walking leg
CC       (PubMed:23895459). {ECO:0000250|UniProtKB:A7RMN1,
CC       ECO:0000269|PubMed:23895459}.
CC   -!- SUBCELLULAR LOCATION: Secreted {ECO:0000269|PubMed:23895459}.
CC       Nematocyst {ECO:0000269|PubMed:23895459}.
CC   -!- PTM: Contains 4 disulfide bonds. {ECO:0000269|PubMed:23895459}.
CC   -!- MASS SPECTROMETRY: Mass=5710.97; Method=MALDI;
CC       Evidence={ECO:0000269|PubMed:23895459};
CC   -!- MISCELLANEOUS: Has no activity on voltage-gated potassium channels
CC       rKv1.4/KCNA4, rKv1.5/KCNA5, rKv2.1/KCNB1, rKv3.1/KCNC1, rKv4.1/KCND1,
CC       rKv4.3/KCND3 channels, hERG/KCNH2, voltage-gated sodium channels
CC       rNav1.2/SCN2A, rNav1.4/SCN4A, and cockroach BgNav1.1.
CC       {ECO:0000269|PubMed:23895459}.
CC   -!- SIMILARITY: Belongs to the sea anemone type 5 potassium channel toxin
CC       family. {ECO:0000305}.
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DR   AlphaFoldDB; C0HJC4; -.
DR   SMR; C0HJC4; -.
DR   TCDB; 8.B.19.1.1; the sea anemone k+ channel blocker toxin, bcstx3 (bcstx3) family.
DR   GO; GO:0005576; C:extracellular region; IDA:UniProtKB.
DR   GO; GO:0042151; C:nematocyst; NAS:UniProtKB.
DR   GO; GO:0019870; F:potassium channel inhibitor activity; IDA:UniProtKB.
DR   GO; GO:0090729; F:toxin activity; IEA:UniProtKB-KW.
DR   GO; GO:0044361; P:negative regulation of voltage-gated potassium channel activity in another organism; IDA:UniProtKB.
PE   1: Evidence at protein level;
KW   Direct protein sequencing; Disulfide bond; Ion channel impairing toxin;
KW   Nematocyst; Neurotoxin; Potassium channel impairing toxin; Secreted; Toxin;
KW   Voltage-gated potassium channel impairing toxin.
FT   CHAIN           1..50
FT                   /note="Kappa-actitoxin-Bcs4a"
FT                   /evidence="ECO:0000269|PubMed:23895459"
FT                   /id="PRO_0000423941"
FT   UNSURE          50
FT                   /note="Q or E-amide"
FT                   /evidence="ECO:0000269|PubMed:23895459"
SQ   SEQUENCE   50 AA;  5718 MW;  329C6B8677E63FE6 CRC64;
     GCKGKYEECT RDSDCCDEKN RSGRKLRCLT QCDEGGCLKY RQCLFYGGLQ