Cystatin SN

Cystatin-1 (CST1) is also known as Cystatin-SN, Cystain-SA-I, Salivary cystatin-SA-1, which is secreted protein and belongs to the cystatin family. Cystatin-1 is expressed in submandibular and sublingual saliva but not in parotid saliva (at protein level) and also expressed in saliva, tears, urine and seminal fluid. Human saliva appears to contain several cysteine proteinase inhibitors that are immunologically related to cystatin S but that differ in their specificity due to amino acid sequence differences. Cystatin SN, with a pI of 7.5, is a much better inhibitor of papain and dipeptidyl peptidase I than is cystatin S, although both inhibit ficin equally well.