Protein Arginine Deiminase

Protein arginine deiminases (PADs) is a unique family of enzymes that catalyzes the hydrolysis of peptidyl-arginine to form peptidyl-citrulline on histones, fibrinogen, and other biologically relevant proteins. In humans, the PAD family is composed of five, calcium dependent isozymes (PADs 1-4 and 6), which share roughly 50% sequence similarity. PADs are found in a myriad of cell and tissue types, including the epidermis and uterus (PAD1), skeletal muscle, brain, inflammatory cells, several cancer cell lines, and secretory glands (PAD2), hair follicles and keratinocytes (PAD3), granulocytes and several types of cancer (PAD4), and oocytes and embryos (PAD6). PAD4, the best characterized isozyme, has also been shown to citrullinate a number of other proteins, including p300, ING4, RPS2, lamin C, and nucleophosmin.