ID   VKTH3_BUNMU             Reviewed;          85 AA.
AC   Q9W728;
DT   16-JUN-2009, integrated into UniProtKB/Swiss-Prot.
DT   01-NOV-1999, sequence version 1.
DT   25-MAY-2022, entry version 66.
DE   RecName: Full=Kunitz-type serine protease inhibitor homolog beta-bungarotoxin B3 chain;
DE   Flags: Precursor;
OS   Bungarus multicinctus (Many-banded krait).
OC   Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Euteleostomi;
OC   Lepidosauria; Squamata; Bifurcata; Unidentata; Episquamata; Toxicofera;
OC   Serpentes; Colubroidea; Elapidae; Bungarinae; Bungarus.
OX   NCBI_TaxID=8616;
RN   [1]
RP   NUCLEOTIDE SEQUENCE [MRNA].
RC   TISSUE=Venom gland;
RX   PubMed=16457863; DOI=10.1016/j.toxicon.2005.11.009;
RA   Cheng Y.-C., Chen K.-C., Lin S.-K., Chang L.-S.;
RT   "Divergence of genes encoding B chains of beta-bungarotoxins.";
RL   Toxicon 47:322-329(2006).
CC   -!- FUNCTION: Beta-bungarotoxins are presynaptic neurotoxins of the venom.
CC       The B chain is homologous to venom basic protease inhibitors but has no
CC       protease inhibitor activity and blocks voltage-gated potassium channels
CC       (Kv) (By similarity). {ECO:0000250}.
CC   -!- SUBUNIT: Heterodimer; disulfide-linked. The A chains have phospholipase
CC       A2 activity and the B chains show homology with the basic protease
CC       inhibitors.
CC   -!- SUBCELLULAR LOCATION: Secreted {ECO:0000250}.
CC   -!- TISSUE SPECIFICITY: Expressed by the venom gland.
CC   -!- SIMILARITY: Belongs to the venom Kunitz-type family. {ECO:0000305}.
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DR   EMBL; AJ242991; CAB44700.1; -; mRNA.
DR   AlphaFoldDB; Q9W728; -.
DR   SMR; Q9W728; -.
DR   GO; GO:0005576; C:extracellular region; IEA:UniProtKB-SubCell.
DR   GO; GO:0015459; F:potassium channel regulator activity; IEA:UniProtKB-KW.
DR   GO; GO:0004867; F:serine-type endopeptidase inhibitor activity; IEA:InterPro.
DR   GO; GO:0090729; F:toxin activity; IEA:UniProtKB-KW.
DR   CDD; cd00109; KU; 1.
DR   Gene3D; 4.10.410.10; -; 1.
DR   InterPro; IPR002223; Kunitz_BPTI.
DR   InterPro; IPR036880; Kunitz_BPTI_sf.
DR   InterPro; IPR020901; Prtase_inh_Kunz-CS.
DR   Pfam; PF00014; Kunitz_BPTI; 1.
DR   PRINTS; PR00759; BASICPTASE.
DR   SMART; SM00131; KU; 1.
DR   SUPFAM; SSF57362; SSF57362; 1.
DR   PROSITE; PS00280; BPTI_KUNITZ_1; 1.
DR   PROSITE; PS50279; BPTI_KUNITZ_2; 1.
PE   2: Evidence at transcript level;
KW   Disulfide bond; Ion channel impairing toxin; Neurotoxin;
KW   Potassium channel impairing toxin; Presynaptic neurotoxin; Secreted;
KW   Signal; Toxin; Voltage-gated potassium channel impairing toxin.
FT   SIGNAL          1..24
FT                   /evidence="ECO:0000250"
FT   CHAIN           25..85
FT                   /note="Kunitz-type serine protease inhibitor homolog beta-
FT                   bungarotoxin B3 chain"
FT                   /id="PRO_5000065301"
FT   DOMAIN          31..81
FT                   /note="BPTI/Kunitz inhibitor"
FT                   /evidence="ECO:0000255|PROSITE-ProRule:PRU00031"
FT   DISULFID        31..81
FT                   /evidence="ECO:0000255|PROSITE-ProRule:PRU00031"
FT   DISULFID        40..64
FT                   /evidence="ECO:0000255|PROSITE-ProRule:PRU00031"
FT   DISULFID        56..77
FT                   /evidence="ECO:0000255|PROSITE-ProRule:PRU00031"
FT   DISULFID        79
FT                   /note="Interchain (with an A chain)"
FT                   /evidence="ECO:0000255|PROSITE-ProRule:PRU00031"
SQ   SEQUENCE   85 AA;  9599 MW;  A333D6EFEDBCDE5C CRC64;
     MSSGGLLLLL GLLTLCAELI PVSSRQRHRD CDKPPDKGNC GPVRRAFYYD TRLKTCKAFQ
     YRGCNGNGNH FKSDHLCRCE CLEYS