Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P56851 (epididymal)
 11,273 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A number of mammalian sperm plasma membrane antigens have been implicated as playing a functional role in sperm-egg interaction, by virtue of the fact that antibodies against these antigens interfere with fertilization. Two such mouse sperm plasma membrane antigens are M42, a 200/220 kD glycoprotein doublet, and M5, a 150-160 kD glycoprotein. We show that both of these antigens are concentrated on the posterior region of caudal epididymal and capacitated mouse sperm heads and are relatively diffusible, as determined by fluorescence recovery after photobleaching measurements (D = 3-8 x 10(-9) cm2/s with approximately 23% diffusing). Crosslinking of these antigens with bivalent antibodies causes them to redistribute into the anterior region (acrosomal crescent) of the sperm head. In contrast, we describe a third antigen, P220, which is also localized to the posterior region of the sperm head on caudal epididymal sperm but which exhibits very little diffusion and does not redistribute upon crosslinking. Bivalent anti-M42 blocks the ZP3-induced acrosome reaction. We have found that monovalent Fab fragments of anti-M42 do not block the ZP3-induced acrosome reaction, but that inhibition is restored by addition of a second antibody which crosslinks the Fabs. Thus, crosslinking is required for both inhibition of the acrosome reaction and redistribution. This suggests that redistribution of antigen away from the posterior region of the head may be part of the mechanism of inhibition of the ZP3-induced acrosome reaction.
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PMID:Protein dynamics in sperm membranes: implications for sperm function during gamete interaction. 141 94

Sperm surface beta 1,4-galactosyltransferase (GalTase) mediates fertilization in mice by binding to specific O-linked oligosaccharide ligands on the egg coat glycoprotein ZP3. Before binding the egg, sperm GalTase is masked by epididymally derived glycosides that are shed from the sperm surface during capacitation. After binding the egg, sperm-bound oligosaccharides on ZP3 induce the acrosome reaction by receptor aggregation, presumably involving GalTase. In this study, we asked how increasing the levels of sperm surface GalTase would affect sperm-egg interactions using transgenic mice that overexpress GalTase under the control of a heterologous promoter. GalTase expression was elevated in many tissues in adult transgenic animals, including testis. Sperm from transgenic males had approximately six times the wild-type level of surface GalTase protein, which was localized appropriately on the sperm head as revealed by indirect immunofluorescence. As expected, sperm from transgenic mice bound more radiolabeled ZP3 than did wild-type sperm. However, sperm from transgenic animals were relatively unable to bind eggs, as compared to sperm from wild-type animals. The mechanistic basis for the reduced egg-binding ability of transgenic sperm was attributed to alterations in two GalTase-dependent events. First, transgenic sperm that overexpress surface GalTase bound more epididymal glycoside substrates than did sperm from wild-type mice, thus masking GalTase and preventing it from interacting with its zona pellucida ligand. Second, those sperm from transgenic mice that were able to bind the zona pellucida were hypersensitive to ZP3, such that they underwent precocious acrosome reactions and bound to eggs more tenuously than did wild-type sperm. These results demonstrate that sperm-egg binding requires an optimal, rather than maximal, level of surface GalTase expression, since increasing this level decreases sperm reproductive efficiency both before and after egg binding. Although sperm GalTase is required for fertilization by serving as a receptor for the egg zona pellucida, excess surface GalTase is counterproductive to successful sperm-egg binding.
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PMID:Overexpressing sperm surface beta 1,4-galactosyltransferase in transgenic mice affects multiple aspects of sperm-egg interactions. 808 87

Guanidinobenzoatase (GB), a proteolytic enzyme found in the epididymal fluids of mice, was purified to apparent homogeneity by molecular sieving and affinity chromatography. It has a molecular mass of 71 kDa and its enzymatic activity is heat labile and sensitive to EGTA. Its kinetic parameters (K(m) of 6.66 microM and a Vmax of 4.38 nmol/min/mg) were determined using 4-methylumbelliferyl-p-guanidinobenzoate (MUGB) as the substrate. GB activity is concentrated in the cauda epididymal region of the genital tract. Heat-solubilized whole zonae, biologically active ZP3, and several serine proteinase inhibitors, including a proteinase inhibitor endogenous to the male genital tract, effectively block the ability of GB to hydrolyze MUGB. Pretreating cumulus-free, zonae intact oocytes with purified GB reduces, in a concentration-dependent manner, the number of sperm able to bind to the zonae. The function of the soluble enzyme is not known. Its ability to bind both trypsin inhibitors and ZP3 suggests a possible role in gamete recognition.
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PMID:Characterization of the guanidinobenzoatase in the epididymal fluids of the mouse. 913 23

Mammalian sperm must undergo a physiological maturation, termed capacitation, before they are able to fertilize eggs. Despite its importance, the molecular mechanisms underlying capacitation are poorly understood. In this paper, we describe the capacitation phenotype of sperm lacking the long isoform of beta1,4-galactosyltransferase I (GalT I), a sperm surface protein that functions as a receptor for the zona pellucida glycoprotein, ZP3, and as an inducer of the acrosome reaction following ZP3-dependent aggregation. As expected, wild-type sperm must undergo capacitation in order to bind the zona pellucida and undergo a Ca(2+) ionophore-induced acrosome reaction. By contrast, GalT I-null sperm behave as though they are precociously capacitated, in that they demonstrate maximal binding to the zona pellucida and greatly increased sensitivity to ionophore-induced acrosome reactions without undergoing capacitation in vitro. The loss of GalT I from sperm results in an inability to bind epididymal glycoconjugates that normally maintain sperm in an 'uncapacitated' state; removing these decapacitating factors from wild-type sperm phenocopies the capacitation behavior of GalT I-null sperm. Interestingly, capacitation of GalT I-null sperm is independent of the presence of albumin, Ca(2+) and HCO(3)(-); three co-factors normally required by wild-type sperm to achieve capacitation. This implies that intracellular targets of albumin, Ca(2+) and/or HCO(3)(-) may be constitutively active in GalT I-null sperm. Consistent with this, GalT I-null sperm have increased levels of cAMP that correlate closely with both the accelerated kinetics and co-factor-independence of GalT I-null sperm capacitation. By contrast, the kinetics of protein tyrosine phosphorylation and sperm motility are unaltered in mutant sperm relative to wild-type. These data suggest that GalT I may function as a negative regulator of capacitation in the sperm head by suppressing intracellular signaling pathways that promote this process.
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PMID:Sperm from beta1,4-galactosyltransferase I-null mice exhibit precocious capacitation. 1469 73

Mammalian fertilization is initiated by species-specific binding of the sperm to the zona pellucida, or egg coat. Previous studies suggested that sperm adhesion to the egg coat is facilitated, at least in part, through the binding of sperm surface beta1 ,4-galactosyltransferase I (GaIT) to glycoside chains on the egg coat glycoprotein, ZP3. Binding of multiple ZP3 oligosaccharides induces aggregation of GaIT within the sperm membrane, triggering, directly or indirectly, a pertussis toxin sensitive G-protein cascade leading to induction of the acrosome reaction. Consistent with this, spermatozoa bearing targeted deletions in GaIT are unable to bind ZP3 or undergo ZP3-dependent acrosomal exocytosis; however, unexpectedly, GaIT-null sperm are still able to bind to the egg coat. This indicates that sperm-egg binding requires at least two independent binding mechanisms; a GaIT-ZP3-independent event that mediates initial adhesion, followed by a GaIT-ZP3 interaction that facilitates acrosomal exocytosis. Our recent efforts have focused on the identification and characterization of these novel gamete receptors. One recently identified sperm protein that is required for sperm adhesion to the egg coat is SED1. SED1 is a bimotif protein composed of two Notch-like EGF repeats and two discoidin/complement F5/8 domains. SED1 is secreted by the epididymal epithelium and coats spermatozoa as they progress through the epididymis. Spermatozoa null for SED1 fail to bind the egg coat, illustrating its requirement for gamete adhesion. Interestingly, SED1 is also expressed by a variety of other epithelial tissues, where it appears to be required for epithelial morphogenesis and/or maintenance. A second novel gamete receptor has recently been identified on the coat of ovulated oocytes. This ZP3-independent, egg coat component is a high molecular weight, wheat germ agglutinin (WGA)-reactive glycoprotein that is derived from oviduct secretions and appears to participate in initial sperm adhesion. The amino acid sequence of this oviduct-derived ligand is currently being determined for the generation of peptide-specific antibodies and for the creation of knock out mice. The identification of novel gamete receptors that are required for sperm-egg binding opens up new avenues for the development of specific contraceptive strategies.
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PMID:Novel gamete receptors that facilitate sperm adhesion to the egg coat. 1756 85

Beta1,4-galactosyltransferase-I (GalTase-I) is one of the key molecules on the sperm surface of eutherian mammals that is likely to be involved in binding to the egg coat, the zona pellucida, to mediate sperm-egg interaction. In laboratory mice, the species for which most data are available, this protein functions as a receptor for the zona pellucida protein ZP3 of the oocyte and, upon binding, triggers the sperm acrosome reaction. In the present study, we investigated the presence and abundance of GalTase-I in epididymal sperm extracts of a marsupial, the brushtail possum, Trichosurus vulpecula. For this, spermatozoa were collected from cauda epididymides and the amount of beta1,4-galactosyltransferase activity in washed sperm extracts was compared with that of porcine spermatozoa. Overall beta1,4-galactosyltransferase enzyme activity was found to be more abundant in possum sperm extracts than those from porcine spermatozoa (P<0.05). Immunoblots with an antibody to mouse GalTase-I revealed that the molecular weight of possum spermatozoa GalTase-I was 66 kDa, which is similar to the molecular weight of GalTase-I in spermatozoa from eutherian mammals. The molecular weight of GalTase-I was the same in sperm extracts collected from the caput and cauda epididymides. These results demonstrate that GalTase-I is indeed present in possum spermatozoa and thus it may be a gamete receptor molecule on the sperm surface of marsupials as well as those of eutherian mammals.
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PMID:Spermatozoa from a marsupial, the brushtail possum, contain beta1,4-galactosyltransferase. 1840 60

Human epididymal CRISP1 (hCRISP1) associates with sperm during maturation and participates in gamete fusion through egg complementary sites. Its homology with both rodent epididymal CRISP1 and CRISP4 reported to participate in the previous stage of sperm binding to the zona pellucida (ZP), led us to further investigate the functional role of hCRISP1 by studying its involvement in human sperm-ZP interaction. Human hemizona (HZ) were inseminated with human capacitated sperm in the presence of either anti-hCRISP1 polyclonal antibody to inhibit sperm hCRISP1, or bacterially-expressed hCRISP1 (rec-hCRISP1) to block putative hCRISP1 binding sites in the ZP. Results revealed that both anti-hCRISP1 and rec-hCRISP1 produced a significant inhibition in the number of sperm bound per HZ compared with the corresponding controls. The finding that neither anti-hCRISP1 nor rec-hCRISP1 affected capacitation-associated events (i.e. sperm motility, protein tyrosine phosphorylation or acrosome reaction) supports a specific inhibition at the sperm-egg interaction level. Moreover, immunofluorescence experiments using human ZP-intact eggs revealed the presence of complementary sites for hCRISP1 in the ZP. To identify the ligand of hCRISP1 in the ZP, human recombinant proteins ZP2, ZP3 and ZP4 expressed in insect cells were co-incubated with hCRISP1 and protein-protein interaction was analyzed by ELISA. Results revealed that rec-hCRISP1 mainly interacted with ZP3 in a dose-dependent and saturable manner, supporting the specificity of this interaction. Altogether, these results indicate that hCRISP1 is a multifunctional protein involved not only in sperm-egg fusion but also in the previous stage of sperm-ZP binding through its specific interaction with human ZP3.
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PMID:Human fertilization: epididymal hCRISP1 mediates sperm-zona pellucida binding through its interaction with ZP3. 2433 45