cystatin 4 (cystatin-S, cystatin-SA3, salivary acidic protein-1, CST4)

Function

• strongly inhibits papain & ficin,
• partially inhibits stem bromelain & bovine cathepsin C
• but does not inhibit porcine cathepsin B or clostripain
• papain is inhibited non-competitively
• phosphorylated at both its N- & C-terminal regions

Structure

belongs to the cystatin family

Compartment

secreted

Expression

found in saliva, tears, urine & seminal fluid

Notes

• human saliva appears to contain several cysteine proteinase inhibitors immunologically related to cystatin S but that differ in their specificity due to amino acid sequence differences

More general terms

• cystatin

Database

• UniProt: http://www.uniprot.org/uniprot/P01036.html
• OMIM: https://mirror.omim.org/entry/123857
• Entrez gene: http://www.ncbi.nlm.nih.gov/sites/entrez?db=gene&cmd=Retrieve&dopt=Graphics&list_uids=1472