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CAP (cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 proteins) domain of cysteine-rich secretory proteins Cysteine-rich secretory proteins (CRISPs) are two-domain proteins with an evolutionary diverse and structurally conserved N-terminal CAP domain and a C-terminal cysteine-rich domain, which is comprised of a hinge and an ICR (ion channel regulator) region. CRISPs are involved in response to pathogens, fertilization, and sperm maturation. One member, Tex31 from the venom duct of Conus textile, has been shown to possess proteolytic activity sensitive to serine protease inhibitors. CRISP-1 has been shown to mediate gamete fusion by binding to the egg surface. Other members of the CRISP family secreted in the testis (CRISP2), epididymis (CRISP3-4), or during ejaculation (CRISP3), are also involved in sperm-egg interaction, supporting the existence of a functional redundancy and cooperation between homolog proteins ensuring the success of fertilization. The wider family of CAP domain containing proteins includes plant pathogenesis-related protein 1 (PR-1) and allergen 5 from vespid venom, among others. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",