Cystatin family

General Activity
Cystatins are inhibitors of cysteine proteinases. They are found in the tissues and body fluids of animals, in the larva of the worm Onchocerca volvulus, as well as in plants. In venom, their role is unknown but they may act as housekeeping or regulatory proteins.

Venom cystatins are expressed at low level (less than 0.6 ug/mg crude venom). In addition, they are similar in terms of weight to phospholipase A2, which in combination with their low molecular weight (13 kDA) makes them difficult to detect (Richards et al., 2011).