Predicted to enable cysteine-type endopeptidase inhibitor activity. Predicted to be involved in negative regulation of endopeptidase activity. Predicted to be active in extracellular space. Orthologous to several human genes including CST5 (cystatin D); CST4 (cystatin S); and CST2 (cystatin SA). [provided by Alliance of Genome Resources, Apr 2022]