The cysteine-rich secretory proteins, antigen 5, and pathogenesis-related 1 proteins (CAP) superfamily members are found in a remarkable range of organisms spanning each of the animal kingdoms. Within humans and mice, there are 31 and 33 individual family members, respectively, and although many are poorly characterized, the majority show a notable expression bias to the reproductive tract and immune tissues or are deregulated in cancers. CAP superfamily proteins are most often secreted and have an extracellular endocrine or paracrine function and are involved in processes including the regulation of extracellular matrix and branching morphogenesis, potentially as either proteases or protease inhibitors; in ion channel regulation in fertility; as tumor suppressor or prooncogenic genes in tissues including the prostate; and in cell-cell adhesion during fertilization. This review describes mammalian CAP superfamily gene expression profiles, phylogenetic relationships, protein structural properties, and biological functions, and it draws into focus their potential role in health and disease. The nine subfamilies of the mammalian CAP superfamily include: the human glioma pathogenesis-related 1 (GLIPR1), Golgi associated pathogenesis related-1 (GAPR1) proteins, peptidase inhibitor 15 (PI15), peptidase inhibitor 16 (PI16), cysteine-rich secretory proteins (CRISPs), CRISP LCCL domain containing 1 (CRISPLD1), CRISP LCCL domain containing 2 (CRISPLD2), mannose receptor like and the R3H domain containing like proteins. We conclude that overall protein structural conservation within the CAP superfamily results in fundamentally similar functions for the CAP domain in all members, yet the diversity outside of this core region dramatically alters target specificity and, therefore, the biological consequences.

The cysteine-rich secretory proteins (Crisp) are predominantly found in the mammalian male reproductive tract as well as in the venom of reptiles. Crisps are two domain proteins with a structurally similar yet evolutionary diverse N-terminal domain and a characteristic cysteine-rich C-terminal domain, which we refer to as the Crisp domain. We presented the NMR solution structure of the Crisp domain of mouse Tpx-1, and we showed that it contains two subdomains, one of which has a similar fold to the ion channel regulators BgK and ShK. Furthermore, we have demonstrated for the first time that the ion channel regulatory activity of Crisp proteins is attributed to the Crisp domain. Specifically, the Tpx-1 Crisp domain inhibited cardiac ryanodine receptor (RyR) 2 with an IC 50 between 0.5 and 1.0 M and activated the skeletal RyR1 with an AC 50 between 1 and 10 M when added to the cytoplasmic domain of the receptor. This activity was nonvoltage-dependent and weakly voltage-dependent, respectively. Furthermore, the Tpx-1 Crisp domain activated both RyR forms at negative bilayer potentials and showed no effect at positive bilayer potentials when added to the luminal domain of the receptor. These data show that the Tpx-1 Crisp domain on its own can regulate ion channel activity and provide compelling evidence for a role for Tpx-1 in the regulation of Ca 2؉ fluxes observed during sperm capacitation.Tpx-1 (testis specific protein-1) was originally identified in the mouse (1) and later found in the male reproductive tract of the human, guinea pig, rat, and horse (2-5). Tpx-1 is a member of the cysteine-rich secretory proteins (Crisp) 2 that are in turn a subgroup of the CAP protein superfamily (abbreviated from Crisp, Antigen 5, and Pr-1 (6)). The CAP proteins each contain a structurally related and unique domain, the CAP domain (7)(8)(9), that at present has no clearly defined biological function, although their spatial and temporal expression suggests a function related to the regulation of the innate immune system (10, 11) and male reproductive function. The Crisp proteins have a characteristic C-terminal sequence containing 10 absolutely conserved cysteines. The Crisp domain is unique and is only observed in association with the CAP domain. Previously, there has been no biological activity attributed specifically to this domain.In mammals, there are at least four Crisp proteins, Crisp-1, Tpx-1 (or Crisp-2), Crisp-3, and Crisp-4. Crisp-1 proteins are expressed predominantly in the epididymides where they coat the surface of sperm during epididymal maturation (12) and have been implicated in sperm oocyte binding and the regulation of capacitation (13-17). Tpx-1 is expressed only in the testis and localized to specific regions in the spermatozoa, notably the acrosome of the head, the outer dense fibers, and longitudinal columns of the fibrous sheath in the sperm tail and the connecting piece of the neck (3, 18). Transfection experiments have also suggested that Tpx-1 is involved in adhesion between germ cells and Sertoli...

Mammalian spermatozoa must undergo capacitation before acquiring the ability to fertilize the oocyte. This process is believed to be initiated following the release of surface-associated decapacitation factors that are elaborated by both the epididymis and the male accessory organs. Herein, we report the identification of a number of proteins that are actively released from the surface of mouse spermatozoa during capacitation in vitro. As anticipated, the addition of these factors back to suspensions of mouse spermatozoa was shown to suppress several correlates of the capacitation process. Specifically, they induced a significant, dose-dependent inhibition of the ability of spermatozoa to undergo a progesterone-induced acrosome reaction and to bind to the zona pellucida in vitro. Inhibition of these functions was associated with the suppression of tyrosine phosphorylation in the sperm plasma membrane but had no effect on the phosphorylation of internal proteins in either the sperm head or tail. This inhibitory activity was attributed to a subset of the isolated proteins compromising at least four putative decapacitation factors. These proteins were identified via tandem-mass spectrometry amino acid sequence analysis as plasma membrane fatty acid binding protein, cysteine-rich secretory protein 1 (CRISP1), phosphatidylethanolamine binding protein 1 (PBP), and an unnamed protein product that we have termed decapacitation factor 10 (DF10). Of these proteins, PBP was identified as a primary candidate for a decapacitation factor.