ID   CYT_BITAR               Reviewed;         111 AA.
AC   P08935;
DT   01-NOV-1988, integrated into UniProtKB/Swiss-Prot.
DT   01-NOV-1988, sequence version 1.
DT   25-MAY-2022, entry version 85.
DE   RecName: Full=Cystatin;
OS   Bitis arietans (African puff adder).
OC   Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Euteleostomi;
OC   Lepidosauria; Squamata; Bifurcata; Unidentata; Episquamata; Toxicofera;
OC   Serpentes; Colubroidea; Viperidae; Viperinae; Bitis.
OX   NCBI_TaxID=8692;
RN   [1]
RP   PROTEIN SEQUENCE, AND VARIANT THR-57.
RC   TISSUE=Venom;
RX   PubMed=3500714; DOI=10.1042/bj2460799;
RA   Ritonja A., Evans H.J., Machleidt W., Barrett A.J.;
RT   "Amino acid sequence of a cystatin from venom of the African puff adder
RT   (Bitis arietans).";
RL   Biochem. J. 246:799-802(1987).
CC   -!- FUNCTION: Inhibits various C1 cysteine proteases including cathepsin L,
CC       papain and cathepsin B. This protein has no toxic activity and its
CC       function in the venom is unknown. It may play a role as housekeeping or
CC       regulatory protein (By similarity). {ECO:0000250}.
CC   -!- SUBCELLULAR LOCATION: Secreted.
CC   -!- TISSUE SPECIFICITY: Expressed by the venom gland.
CC   -!- SIMILARITY: Belongs to the cystatin family. {ECO:0000305}.
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DR   PIR; A28793; A28793.
DR   AlphaFoldDB; P08935; -.
DR   SMR; P08935; -.
DR   MEROPS; I25.012; -.
DR   GO; GO:0005576; C:extracellular region; IEA:UniProtKB-SubCell.
DR   GO; GO:0004869; F:cysteine-type endopeptidase inhibitor activity; IEA:UniProtKB-KW.
DR   CDD; cd00042; CY; 1.
DR   InterPro; IPR000010; Cystatin_dom.
DR   InterPro; IPR046350; Cystatin_sf.
DR   InterPro; IPR018073; Prot_inh_cystat_CS.
DR   Pfam; PF00031; Cystatin; 1.
DR   SMART; SM00043; CY; 1.
DR   SUPFAM; SSF54403; SSF54403; 1.
DR   PROSITE; PS00287; CYSTATIN; 1.
PE   1: Evidence at protein level;
KW   Direct protein sequencing; Disulfide bond; Protease inhibitor; Secreted;
KW   Thiol protease inhibitor.
FT   CHAIN           1..111
FT                   /note="Cystatin"
FT                   /id="PRO_0000207152"
FT   DOMAIN          3..103
FT                   /note="Cystatin"
FT   MOTIF           47..51
FT                   /note="Secondary area of contact"
FT   SITE            3
FT                   /note="Reactive site"
FT   DISULFID        65..81
FT                   /evidence="ECO:0000305"
FT   VARIANT         57
FT                   /note="M -> T"
FT                   /evidence="ECO:0000269|PubMed:3500714"
SQ   SEQUENCE   111 AA;  12678 MW;  1A31B6B246ACA10C CRC64;
     IPGGLSPRDV TDPDVQEAAA FAVEKYNAGS KNDYYFKERR VVEAQSQVVS GVKYYLMMEL
     LKTTCKKTVG RPKGYQEIQN CNLPPENQQE EITCRFEVWS RPWLPSTSLT K