Cysteine-rich secretory protein, SCP domain (IPR034117)

Short name: SCP_CRISP

Overlapping homologous superfamilies

Domain relationships

  • CAP domain (IPR014044)
    • Cysteine-rich secretory protein, SCP domain (IPR034117)


This SCP-like extracellular protein domain is found in cysteine-rich secretory proteins (CRISPs). Involvement of CRISP in response to pathogens, fertilization, and sperm maturation have been proposed [PMID: 17644975, PMID: 17644967, PMID: 16414181]. One member, Tex31 from the venom duct of Conus textile, has been shown to possess proteolytic activity sensitive to serine protease inhibitors [PMID: 12759345]. SCP has also been proposed to be a Ca++ chelating serine protease. The Ca++-chelating function would fit with various signaling processes that members of this family, such as the CRISPs, are involved in, and is supported by sequence and structural evidence of a conserved pocket containing two histidines and a glutamate. It also may explain how helothermine, a toxic peptide secreted by the beaded lizard, blocks Ca++ transporting ryanodine receptors [PMID: 7647234]. One member, DE or CRISP-1, has been shown to mediate gamete fusion by binding to the egg surface; a sequence motif in the SCP domain plays a role in that binding [PMID: 16872593].

The SCP domain is also known as CAP domain [PMID: 18824526]. The wider family of SCP containing proteins includes plant pathogenesis-related protein 1 (PR-1), CRISPs, mammalian cysteine-rich secretory proteins, which combine SCP with a C-terminal cysteine rich domain, and allergen 5 from vespid venom. It has been proposed that SCP domains may function as endopeptidases.

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.