Cysteine proteinase inhibitor that possibly plays a protective role against proteinases present in the oral cavity. The order of preference for inhibition is cathepsin S > cathepsin H > cathepsin L > cathepsin B. Thermostable. Monomer. Expressed in submandibular and sublingual saliva but not in parotid saliva (at protein level). Expressed in parotid gland but not in seminal vesicle, prostate, epididymis, testis, ovary, placenta, thyroid, gastric corpus, small intestine, liver, or gall bladder tissue. Variant Arg-46. Variant Arg-46. Belongs to the cystatin family. The truncated forms found may result from N-terminal proteolysis.