ID   CYT_NAJAT               Reviewed;          99 AA.
AC   P81714;
DT   26-SEP-2001, integrated into UniProtKB/Swiss-Prot.
DT   01-JUN-2001, sequence version 1.
DT   25-MAY-2022, entry version 67.
DE   RecName: Full=Cystatin;
DE   Flags: Fragment;
OS   Naja atra (Chinese cobra).
OC   Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Euteleostomi;
OC   Lepidosauria; Squamata; Bifurcata; Unidentata; Episquamata; Toxicofera;
OC   Serpentes; Colubroidea; Elapidae; Elapinae; Naja.
OX   NCBI_TaxID=8656;
RN   [1]
RP   PROTEIN SEQUENCE, AND FUNCTION.
RC   TISSUE=Venom;
RX   PubMed=9512485; DOI=10.1042/bj3310239;
RA   Brillard-Bourdet M., Nguyen V., Ferrer-Di Martino M., Gauthier F.,
RA   Moreau T.;
RT   "Purification and characterization of a new cystatin inhibitor from Taiwan
RT   cobra (Naja naja atra) venom.";
RL   Biochem. J. 331:239-244(1998).
CC   -!- FUNCTION: Inhibits various C1 cysteine proteases including cathepsin L
CC       (Ki is 0.1 nM), papain (Ki is 0.19 nM), cathepsin S (Ki is 1.2 nM), and
CC       cathepsin B (Ki is 2.5 nM). 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. {ECO:0000269|PubMed:9512485}.
CC   -!- SUBCELLULAR LOCATION: Secreted.
CC   -!- TISSUE SPECIFICITY: Expressed by the venom gland.
CC   -!- MISCELLANEOUS: Does not inhibit calpain. {ECO:0000305|PubMed:9512485}.
CC   -!- SIMILARITY: Belongs to the cystatin family. {ECO:0000305}.
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DR   AlphaFoldDB; P81714; -.
DR   SMR; P81714; -.
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   Pfam; PF00031; Cystatin; 1.
DR   SMART; SM00043; CY; 1.
DR   SUPFAM; SSF54403; SSF54403; 1.
PE   1: Evidence at protein level;
KW   Direct protein sequencing; Disulfide bond; Protease inhibitor; Secreted;
KW   Thiol protease inhibitor.
FT   CHAIN           1..>99
FT                   /note="Cystatin"
FT                   /id="PRO_0000207153"
FT   DOMAIN          3..>99
FT                   /note="Cystatin"
FT   MOTIF           47..51
FT                   /note="Secondary area of contact"
FT                   /evidence="ECO:0000250"
FT   SITE            3
FT                   /note="Reactive site"
FT                   /evidence="ECO:0000250"
FT   DISULFID        65..81
FT                   /evidence="ECO:0000250"
FT   DISULFID        94..?
FT                   /evidence="ECO:0000250"
FT   NON_TER         99
SQ   SEQUENCE   99 AA;  10995 MW;  7F3696E0D60B3974 CRC64;
     IPGGLSPRSV SDPDVQKAAA FAVQEYNAGS ANAHYYKELR VVEAQSQSVA GEKYFLMMEL
     VKTKCAKTAG KPKVYKEIQN CELPPIKQQE EKLCGFQVW