The PLAC (protease and lacunin) domain is a six-cysteine region of about 40 residues that is present at or near the C-terminal of various enzymes and matrix proteins, including: mammalian PACE4 (paired basic amino acid cleaving enzyme 4), mammalian PCSK5 (proprotein convertase subtilisin/kexin type 5), mammalian metalloproteinases ADAMTS-2, -3, -10, -12, -14, -16, -17, and -19, and manduca Sexta matrix protein lacunin []. The PLAC domain is often associated with other domains, such as the thrombospondin type I repeat (TSP1) (), the Kunitz proteinase inhibitor domain (), the Ig-like domain (), the WAP domain (), the subtilase domain (), or the ADAM-type metalloprotease domain ().