{PDOC00259}
{PS00287; CYSTATIN}
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* Cysteine proteases inhibitors signature *
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Inhibitors of cysteine  proteases [1,2,3],  which are found in the tissues and
body fluids of animals,  in the larva of the worm Onchocerca volvulus [4],  as
well as in plants, can be grouped into three distinct but related families:

 - Type 1 cystatins (or stefins), molecules of  about 100 amino  acid residues
   with neither disulfide bonds nor carbohydrate groups.
 - Type 2 cystatins, molecules of about 115  amino acid residues which contain
   one or two disulfide loops near their C-terminus.
 - Kininogens, which are  multifunctional  plasma glycoproteins.  They are the
   precursor  of  the  active  peptide  bradykinin  and  play  a role in blood
   coagulation by  helping  to  position optimally prekallikrein and factor XI
   next  to factor XII.  They  are  also  inhibitors  of  cysteine  proteases.
   Structurally,  kininogens  are  made  of  three  contiguous type-2 cystatin
   domains, followed  by an  additional  domain  (of  variable  length)  which
   contains  the  sequence of bradykinin.  The  first  of  the  three cystatin
   domains seems to have lost its inhibitory activity.

In all  these  inhibitors,  there is a conserved region of five residues which
has been proposed to be  important for  the binding to the cysteine proteases.
Our pattern starts one residue before this conserved region.

-Consensus pattern: [GSTEQKRV]-Q-[LIVT]-[VAF]-[SAGQ]-G-{DG}-[LIVMNK]-{TK}-x-
                    [LIVMFY]-{S}-[LIVMFYA]-[DENQKRHSIV]
-Sequences known to belong to this class detected by the pattern: ALL.
-Other sequence(s) detected in Swiss-Prot: 11.

-Note: This pattern is always twice in kininogens.
-Note: Members  of the fetuin family (see <PDOC00966>) contain two copies of a
 cystatin-like domain.

-Expert(s) to contact by email:
           Turk B.; boris.turk@ijs.si

-Last update: April 2006 / Pattern revised.

[ 1] Barrett A.J.
     Trends Biochem. Sci. 12:193-196(1987).
[ 2] Rawlings N.D., Barrett A.J.
     "Evolution of proteins of the cystatin superfamily."
     J. Mol. Evol. 30:60-71(1990).
     PubMed=2107324
[ 3] Turk V., Bode W.
     "The cystatins: protein inhibitors of cysteine proteinases."
     FEBS Lett. 285:213-219(1991).
     PubMed=1855589
[ 4] Lustigman S., Brotman B., Huima T., Prince A.M.
     "Characterization of an Onchocerca volvulus cDNA clone encoding a
     genus specific antigen present in infective larvae and adult worms."
     Mol. Biochem. Parasitol. 45:65-75(1991).
     PubMed=2052041

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