Ability of sulfated glycoconjugates and disulfide-reductants to release bovine epididymal sperm bound to the oviductal epithelium in vitro

In Bos taurus, at ejaculation, epididymal sperm acquire a number of proteins secreted in the seminal plasma that increase their ability to interact with the female reproductive tract. Sperm-oviduct interaction comprises a transient sperm adhesion to the isthmus, the lower portion of the oviduct, followed by sperm release around ovulation. Oviductal fluid molecules, such as sulfated glycoconjugates and disulfide-reductants, are able to release bovine ejaculated sperm bound to the oviductal epithelium in vitro through the reduction of sperm surface protein disulfides to sulfhydryls. To understand whether the sperm molecules sensitive to releasing signals are already exposed on the surface of epididymal sperm, we studied the ability of cauda epididymal sperm to adhere to the oviductal epithelium and to be released by sulfated glycoconjugates and the disulfide-reductant penicillamine. Surface protein sulfhydryls in cauda epididymal sperm were analyzed in the initial suspension, in sperm bound to the in vitro-cultured oviductal epithelium, and in released sperm. Results showed that epididymal sperm are able to bind the oviductal epithelium in vitro, although at a lower extent than frozen-thawed ejaculated sperm; the interaction is mediated by oviductal cell microvilli that closely bind to the plasma membrane of the sperm head rostral region, as previously shown for ejaculated sperm. The sulfated glycoconjugates heparin, fucoidan, and dextran sulfate, as well as the disulfide-reductant penicillamine, are all powerful inducers of sperm release. The level of sulfhydryls in sperm surface proteins was (1) high in the initial sperm suspension; (2) low in bound sperm; (3) markedly increased in sperm released by heparin or by penicillamine. In conclusion, epididymal sperm are already able to bind the oviductal epithelium and to respond to the inducers of release through the reduction of sperm surface protein disulfides to sulfhydryls.     

Malaria sporozoites and circumsporozoite proteins bind specifically to sulfated glycoconjugates

Circumsporozoite (CS) proteins, which densely coat malaria (Plasmodia) sporozoites, contain an amino acid sequence that is homologous to segments in other proteins which bind specifically to sulfated glycoconjugates. The presence of this homology suggests that sporozoites and CS proteins may also bind sulfated glycoconjugates. To test this hypothesis, recombinant P. yoelii CS protein was examined for binding to sulfated glycoconjugate-Sepharoses. CS protein bound avidly to heparin-, fucoidan-, and dextran sulfate-Sepharose, but bound comparatively poorly to chondroitin sulfate A- or C-Sepharose. CS protein also bound with significantly lower affinity to a heparan sulfate biosynthesis-deficient mutant cell line compared with the wild-type line, consistent with the possibility that the protein also binds to sulfated glycoconjugates on the surfaces of cells. This possibility is consistent with the observation that CS protein binding to hepatocytes, cells invaded by sporozoites during the primary stage of malaria infection, was inhibited by fucoidan, pentosan polysulfate, and heparin. The effects of sulfated glycoconjugates on sporozoite infectivity were also determined. P. berghei sporozoites bound specifically to sulfatide (galactosyl[3-sulfate]beta 1-1ceramide), but not to comparable levels of cholesterol-3-sulfate, or several examples of neutral glycosphingolipids, gangliosides, or phospholipids. Sporozoite invasion into hepatocytes was inhibited by fucoidan, heparin, and dextran sulfate, paralleling the observed binding of CS protein to the corresponding Sepharose derivatives. These sulfated glycoconjugates blocked invasion by inhibiting an event occurring within 3 h of combining sporozoites and hepatocytes. Sporozoite infectivity in mice was significantly inhibited by dextran sulfate 500,000 and fucoidan. Taken together, these data indicate that CS proteins bind selectively to certain sulfated glycoconjugates, that sporozoite infectivity can be inhibited by such compounds, and that invasion of host hepatocytes by sporozoites may involve interactions with these types of compounds.     

Thrombospondin related anonymous protein (TRAP) of Plasmodium falciparum binds specifically to sulfated glycoconjugates and to HepG2 hepatoma cells suggesting a role for this molecule in sporozoite invasion of hepatocytes.

Thrombospondin related anonymous protein (TRAP) of Plasmodium falciparum contains an amino acid motif based around the sequence WSPCSVTCG which is also found in region II of the circumsporozoite (CS) proteins of different species of Plasmodium. This amino acid motif confers on the CS protein the ability to bind specifically to sulfated glycoconjugates and to hepatocytes. This suggests that the interaction of CS protein with sulfated glycoconjugates on the surface of the hepatocytes may represent the first molecular event of sporozoite invasion of liver cells. Experimental evidence indicates that TRAP is localized both on the micronemes and on the surface of P. falciparum sporozoites implying that TRAP with its putative sulfated glycoconjugate binding motif may also be involved in recognition and/or entry of hepatocytes by the sporozoite. We show here that different TRAP constructs expressed in Escherichia coli bind to sulfogalactosyl-cerebrosides (sulfatides) and to the surface of HepG2 cells. These interactions are dependent on the presence of the conserved amino acid motif WSPCSVTCG within the sequences of the constructs and are completely inhibited by several sulfated glycoconjugates as well as by suramin, a polysulfonated drug with anti-protozoan activity. Moreover, sporozoite invasion of HepG2 cells is inhibited by antisera raised against these different TRAP constructs and by the presence of low concentrations of suramin. We concluded that TRAP may be one of the parasite encoded molecules in the host-parasite interaction that results in sporozoite invasion of hepatocytes.     

THE FUCUS (PHAEOPHYCEAE) SPERM RECEPTOR FOR EGGS. I. DEVELOPMENT AND CHARACTERISTICS OF A BINDING ASSAY1

To explore the molecular basis of egg-sperm recognition in the brown alga , Fucus serratus L., we developed an in vitro binding assay involving egg plasma membrane vesicles (PMVs) and proteins contained in a KCl extract of sperm. Binding between the two components was measured using biotinylated PMVs followed by the addition of streptavidin conjugated to alkaline phosphatase and the appropriate substrate. Biotinylation did not affect the ability of egg PMVs to inhibit fertilization in a species-preferential manner. Binding of labeled egg PMVs to the sperm KCl extract was saturable and competable with unlabeled PMVs but was not species-specific. Protease treatment of the KCl extract abolished binding, whereas periodate had no effect, suggesting that sperm protein rather than carbohydrate was involved. Preincubation of the sperm extract with sulfated polysaccharides (e.g. fucoidan and ascophyllan) inhibited binding of egg plasma membranes. Sulfation seems to be important for this effect since desulfated fucoidan was far less effective at blocking binding. Polysaccharides which inhibited binding also inhibited fertilization. Overall, the results indicate that at least some aspects of binding between Fucus sperm and eggs are mediated by a protein(s) derived from sperm which recognizes sulfated glycoconjugates on the egg plasma membrane .     

Effect of sulfated glycoconjugates on capacitation and the acrosome reaction of bovine and hamster spermatozoa

The effects of sulfated glycoconjugates on the preparation of mammalian sperm for fertilization were investigated. The three sulfated glycoconjugates tested were heparin, dextran sulfate, and the fucose sulfate glycoconjugate (FSG) from the sea urchin egg jelly coat. In vivo, FSG induces the acrosome reaction in sea urchin sperm. Bovine sperm were found to be capacitated by heparin and FSG as judged both by ability of lysophosphatidylcholine (LC) to induce an acrosome reaction and by ability to fertilize bovine oocytes in vitro. The mechanism by which heparin or FSG capacitated bovine sperm appeared similar, since glucose inhibited capacitation by both glycoconjugates. In contrast to effects on bovine sperm, heparin and FSG induced the acrosome reaction in capacitated hamster sperm. When hamster sperm were incubated under noncapacitating conditions, heparin had no effect on capacitation or the acrosome reaction. Three molecular weights (MW) of dextran sulfate (5,000, 8,000, 500,000) were found to capacitate bovine sperm as judged by the ability of LC to induce an acrosome reaction. Whereas bovine sperm incubated with 5,000 or 8,000 M W dextran sulfate fertilized more bovine oocytes than control sperm (P <0.05), sperm treated with 500,000 M W dextran sulfate failed to penetrate oocytes. The high-MW dextran sulfate appeared to interact with the zona pellucida and/or sperm to prevent sperm binding. Results suggest that sulfated glycoconjugates may prepare sperm for fertilization across a wide range of species.     

Sulfated glycoconjugates are powerful modulators of bovine sperm adhesion and release from the oviductal epithelium in vitro

The mechanisms of sperm adhesion and release within the mammalian oviduct are still poorly understood. In this in vitro study, a previously developed adhesion assay was used to analyze the effects of heparin, N-desulfated heparin, fucoidan, dextran sulfate, and dextran on bovine sperm-oviductal cell adhesion and release. Results showed that 1) all sulfated glycoconjugates were powerful inhibitors of sperm binding to oviductal monolayers in a dose-dependent manner, whereas N-desulfated heparin and dextran had no effect; 2) sperm pretreatment with heparin and fucoidan markedly inhibited adhesion; 3) treatment of oviductal monolayers with heparinase I, II, or sodium chlorate (an inhibitor of sulfation) had no effect on sperm adhesion; 4) sulfated glycoconjugates were also powerful and quick inducers of sperm release from oviductal monolayers; and 5) addition of sulfated glycoconjugates to the cocultures caused a sudden increase of bound-sperm flagellar beat frequencies, followed by a release of highly motile sperm. In conclusion, these data support the hypothesis that sulfated glycoconjugates may act as signals that induce sperm release and migration from the oviductal reservoir.     

Interactions of a laminin-binding peptide from a 33-kDa protein related to the 67-kDa laminin receptor with laminin and melanoma cells are heparin-dependent.

A laminin-binding peptide (peptide G), predicted from the cDNA sequence for a 33-kDa protein related to the 67-kDa laminin receptor, specifically inhibits binding of laminin to heparin and sulfatide. Since the peptide binds directly to heparin and inhibits interaction of another heparin-binding protein with the same sulfated ligands, this inhibition is due to direct competition for binding to sulfated glycoconjugates rather than an indirect effect of interaction with the binding site on laminin for the 67-kDa receptor. Direct binding of laminin to the peptide is also inhibited by heparin. This interaction may result from contamination of the laminin with heparan sulfate, as binding is enhanced by the addition of substoichiometric amounts of heparin but inhibited by excess heparin and two heparin-binding proteins. Furthermore, laminin binds more avidly to a heparin-binding peptide derived from thrombospondin than to the putative receptor peptide. Adhesion of A2058 melanoma cells on immobilized peptide G is also heparin-dependent, whereas adhesion of the cells on laminin is not. Antibodies to the beta 1-integrin chain or laminin block adhesion of the melanoma cells to laminin but not to peptide G. Thus, the reported inhibition of melanoma cell adhesion to endothelial cells by peptide G may result from inhibition of binding of laminin or other proteins to sulfated glycoconjugate receptors rather than from specific inhibition of laminin binding to the 67-kDa receptor.     

Carbohydrate specificity of sea urchin sperm bindin: a cell surface lectin mediating sperm-egg adhesion

We have examined the carbohydrate specificity of bindin, a sperm protein responsible for the adhesion of sea urchin sperm to eggs, by investigating the interaction of a number of polysaccharides and glycoconjugates with isolated bindin. Several of these polysaccharides inhibit the agglutination of eggs by bindin particles. An egg surface polysaccharide was found to be the most potent inhibitor of bindin- mediated egg agglutination. Fucoidin, a sulfated fucose heteropolysaccharide, was the next most potent inhibitor, followed by the egg jelly fucan, a sulfated fucose homopolysaccharide, and xylan, a beta(1 leads to 4) linked xylose polysaccharide. A wide variety of other polysaccharides and glycoconjugates were found to have no effect on egg agglutination. We also report that isolated bindin has a soluble lectinlike activity which is assayed by agglutination of erythrocytes. The bindin lectin activity is inhibited by the same polysaccharides that inhibit egg agglutination by particulate bindin. This suggests that the egg adhesion activity of bindin is directly related to its lectin activity. We have established that fucoidin binds specifically to bindin particles with a high apparent affinity (Kd = 5.5 X 10(-8) M). The other polysaccharides that inhibit egg agglutination also inhibit the binding of 125I-fucoidin to bindin particles, suggesting that they compete for the same site on bindin. The observation that polysaccharides of different composition and linkage type interact with bindin suggests that the critical structural features required for binding may reside at a higher level of organization. Together, these findings strengthen the hypothesis that sperm-egg adhesion in sea urchins is mediated by a lectin-polysaccharide type of interaction.     

Specific recognition of sulfate esters by bindin, a sperm adhesion protein from sea urchins

Bindin specifically binds to egg surface sulfated fucan polysaccharides and mediates the attachment of sperm to the egg during fertilization. Sulfate esters are critical for this interaction. We have examined the effect of different anionic groups on the relative binding affinities of a series of homologous anionic polymers for bindin to determine the extent to which other charged moieties can substitute for sulfate. We found that bindin displays a remarkable specificity for sulfate- or sulfonic acid-containing polymers. The relative affinities of poly(vinyl sulfate) and poly(styrenesulfonic acid) are four orders of magnitude higher than polymers containing phosphate esters or carboxyl groups. The bindin-mediated aggregation of sea urchin eggs was inhibited by the sulfated polymers but not the other anionic polymers. This high degree of selectivity for sulfated polymers is not observed for the binding of the polyanions to most other proteins and basic polypeptides. These results suggest that the binding is not due to the formation of simple salt bridges, and that all three non-ester oxygen atoms of the sulfate groups are involved in multiple bonding interactions with a complementary 'docking site' on the bindin polypeptide. The orientation of the polysaccharide sulfate oxygen atoms relative to the protein binding site may be an important determinant of the specificity of polysaccharide binding.     

Antistasin, an inhibitor of coagulation and metastasis, binds to sulfatide (Gal(3-SO4) beta 1-1Cer) and has a sequence homology with other proteins that bind sulfated glycoconjugates

Antistasin, a 15-kDa salivary protein from the Mexican leech Haementeria officinalis, inhibits both blood coagulation and the metastasis of tumors (Tuszynski, G. P., Gasic, T. B., and Gasic, G. J. (1987) J. Biol. Chem. 262, 9718-9723). Antistasin binds to heparin-agarose, suggesting the protein interacts with sulfated glycoconjugates. The specificity of the interaction between antistasin and heparin was tested by measuring the binding of antistasin to various lipids and by comparing the ability of several charged glycoconjugates to inhibit binding. Of the lipids tested, antistasin binds with high affinity only to sulfatide (Gal(3-SO4)beta 1-1Cer) and does not bind to comparable levels of phospholipids, neutral glycosphingolipids, gangliosides, or cholesterol-3-SO4. The binding of antistasin to sulfatide is inhibited by dextran sulfate, fucoidan, and heparin, with I50 values of 1.5, 9.2, and 16 micrograms/ml, respectively. Comparable levels of chondroitin sulfates A, B, C, keratan sulfate, or hyaluronic acid do not inhibit binding. Comparisons of the amino acid sequences of antistasin and other sulfatide or heparin-binding proteins revealed a region of homology, based around the sequence Cys-Ser-Val-Thr-Cys-Gly-X-Gly-X-X-X-Arg-X-Arg, which may be a sulfated glycoconjugate binding domain. In addition, homologies were found with the alternate complement pathway protein properdin and coat proteins from malaria circumsporozoites and Herpes simplex I.     

Properdin binds to sulfatide [Gal(3-SO4)beta 1-1 Cer] and has a sequence homology with other proteins that bind sulfated glycoconjugates

Properdin, which stabilizes the C3 convertase during the activation of the alternate complement pathway, contains amino acid sequence homologies with several proteins that bind sulfated glycoconjugates, including the adhesive protein thrombospondin and the leech salivary protein antistasin. This homology is based around the sequence Cys-Ser-Val-Thr-Cys-Gly-X-Gly-X-X-X-Arg-X-Arg. To determine if these homologous amino acid sequences are sulfated glycoconjugate-binding domains, purified native properdin, as well as activated properdin (a high molecular weight form of properdin), were examined for binding to various lipids in solid phase radioimmunoassays. Of the lipids tested, both native and activated properdin bind with high affinity only to sulfatide [Gal(3-SO4)beta 1-1 Cer], but not to comparable levels of cholesterol-3-SO4, or several neutral glycolipids, gangliosides, and phospholipids. Sulfatide binding by both forms of properdin is inhibited by dextran sulfate (Mr = 500,000) or fucoidan, whereas only the activated form is inhibited by dextran sulfate (Mr = 5,000) or heparin. Comparable levels of chondroitin sulfates A, B, and C, keratan sulfate, dextran (Mr = 90,000), or hyaluronic acid do not inhibit binding. Taken together, these data suggest that properdin, like antistasin and thrombospondin, binds sulfated glycoconjugates and supports the conclusion that the homologous sequences are sulfated glycoconjugate-binding domains.     

Sperm binding to oviductal epithelial cells in the rat: role of sialic acid residues on the epithelial surface and sialic acid-binding sites on the sperm surface

The aim of this study was to assess the participation of carbohydrate residues in the adhesion of spermatozoa to the oviductal epithelium in the rat. We first examined, by lectin labeling, the distribution of glycoconjugates in rat oviducts obtained under various hormonal environments. Several classes of glycoconjugates were abundant in the epithelium, and the expression of some of these molecules varied differentially in ampulla and isthmus, along the estrous cycle and with estradiol and progesterone treatment. Proestrous rats were intraoviductally injected with lectins Dolichos biflorus, Erythrina cristagalli, Helix pomatia, Arachis hypogea, Ulex europaeus I, Triticum vulgaris, or Tritrichomonas mobilensis and were inseminated with 10-20 million epididymal spermatozoa in each uterine horn. Three hours later, the total number of spermatozoa present in the oviduct and the proportion adhering to the epithelium were determined. Intraoviductal administration of lectins did not affect the total number of spermatozoa recovered from the oviduct and only the sialic acid-binding lectin TML decreased the percentage of sperm cells adhering to the epithelium. The involvement of sialic acid in sperm-oviduct adhesion was further explored, inseminating spermatozoa preincubated with mannose, galactose, sialic acid, fucose, fetuin, or asialofetuin. Sialic acid and fetuin inhibited sperm-oviduct binding while other carbohydrates had no effect. Using TML lectin immunohistochemistry, we found that sialic acid-rich glycoconjugates are equally localized in the epithelium of ampulla and isthmus of proestrous rats. The electrophoretic pattern of sialic acid-rich glycoproteins of the epithelium showed 15 major protein bands, for which molecular mass ranged from 200 to 50 kDa with no difference between ampulla and isthmus or between estrous cycle stages. Binding sites for sialic acid-fluorescein isothiocyanate were demonstrated on the surface of rat spermatozoa, and biotinylated sialic acid recognized 11 plasma membrane proteins of sperm cells. These groups of sialic acid-rich glycoproteins in the oviductal epithelium and of sialic acid-binding proteins in the plasma membrane of sperm cells are good candidates for further studies to characterize the molecules responsible for sperm binding. We conclude that there are segment-specific changes of sugar residues present in the oviductal epithelium associated with different endocrine environments. Sperm-oviduct adhesion in the rat occurs by interaction of sialoglycoconjugates present in the epithelial cells with sialic acid-binding proteins on the sperm surface. This replicates the situation previously found in hamsters, disclosing for the first time that species-specificity in the sugar involved in sperm binding is not absolute.     

Isolation, composition, and biological activity of sugar chains of porcine oocyte zona pellucida 55K glycoproteins

ZP3, a preparation of the 55K families of porcine oocyte zona pellucida, possesses carbohydrate-dependent ligand activity for boar sperm. The aim of the present study was to analyze ZP3 N- and O-linked oligosaccharides with respect to size distribution, composition, and role in sperm-zona recognition events. Digestion of denatured ZP3 with peptide N-glycosidase F (PNGaseF) released the majority of N-glycans which fractionated on Sephadex G-75 resin as a polydisperse population with apparent molecular masses ranging from 1,900-8,200 Da. The higher molecular weight N-glycans were characterized by the presence of strongly anionic sulfated/sialylated polylactosamine structures. Alkaline-borohydride treatment of the PNGaseF-digested core proteins liberated O-glycans as a heterogeneous population of oligosaccharide alcohols, which were fractionated on a Sephadex G-50 column. Compositional analyses indicated sulfated polylactosamine units associated with the higher molecular weight O-glycans. Preincubation of boar sperm with ZP3 or purified O-glycans, but not N-glycans, inhibited subsequent attachment to zona-encased oocytes. Purified O-glycans were, however, 2 to 3 orders of magnitude less effective than ZP3 as competitive ligands. The results document the extreme heterogeneity of the ZP3 carbohydrate moiety, in large part attributable to a broad spectrum of variably sized N- and O-linked sulfated polylactosamines. Ligand competition bioassays suggest that O-glycans mediate, at least in part, the sperm adhesive properties of ZP3 and strongly imply that high-affinity interaction of ZP3 sugar chains with complementary sperm receptors is dependent upon their covalent association with core proteins.     

Protein-carbohydrate complementarity in mammalian gamete recognition

Recent studies suggest that gamete recognition in a number of species is mediated by complementary proteins and carbohydrates on opposing gamete surfaces. Studies in invertebrates and vertebrates have shown that carbohydrate-binding proteins on the sperm surface recognize and bind to complementary glycoconjugates on the egg's extracellular coat. This chapter reviews our current knowledge of gamete recognition in the mouse. The complementary receptors for both mouse sperm and egg have been identified, purified, and characterized. Their synthesis during gametogenesis has been defined, as have the effects of sperm capacitation and of the acrosome reaction on their expression and distribution. Their relationship to gamete receptors that function in other species is discussed. Finally, evidence is presented that suggests that one of the receptors that mediate mouse gamete recognition belongs to a family of cell surface receptors that function during multiple cellular interactions in development.     

The interaction of boar sperm proacrosin with its natural substrate, the zona pellucida, and with polysulfated polysaccharides

Boar sperm acrosin is an acrosomal protease with trypsin-like specificity, and it functions in fertilization by assisting sperm passage through the zona pellucida by limited hydrolysis of this extracellular matrix. In addition to a proteolytic active site domain, acrosin binds the zona pellucida at a separate binding domain that is lost during proacrosin autolysis. In this study, we quantitate the binding of proacrosin to the physiological substrate for acrosin, the zona pellucida, and to a non-substrate, the polysulfated polysaccharide fucoidan. Binding was analogous to sea urchin sperm bindin that binds egg jelly fucan and the vitelline envelope of sea urchin eggs. Proacrosin was found to bind to fucoidan and to the zona pellucida with binding affinities similar to bindin interaction with egg jelly fucan. These interactions were competitively inhibited by similar relative molecular mass polysulfated polymers. Since bindin and proacrosin have distinctly different amino acid sequences, their interaction with acidic sulfate esters demonstrates an example of convergent evolution wherein different macromolecules localized in analogous sperm compartments have the same biological function. From cDNA sequence analysis of proacrosin, this binding may be mediated through a consensus sequence for binding sulfated glycoconjugates. Proacrosin binding to the zona pellucida may serve as both a recognition or primary sperm receptor, as well as maintaining the sperm on the zona pellucida once the acrosome reaction has occurred.     

Separation, characterization and identification of boar seminal plasma proteins

Methods used for the isolation, separation and characterization of boar seminal plasma proteins are discussed, as well as techniques applied to study their binding properties. Attention is paid to interactions of these proteins with different types of saccharides and glycoconjugates, with membrane phospholipids, and to interactions between proteins. Boar seminal plasma contains different types of proteins: spermadhesins of the AQN and AWN families; DQH and PSP proteins belong to the most abundant. Some of these proteins are bound to the sperm surface during ejaculation and thus protein-coating layers of sperm are formed. Sperms coated with proteins participate in different types of interactions occurring in the course of the reproduction process, e.g. formation of the oviductal sperm reservoir, sperm capacitation, oocyte recognition and sperm binding to the oocyte.     

精子膜表面蛋白的研究进展

动物的精子是一类结构和功能都十分特化的细胞,其膜表面存在多种糖蛋白或糖复合物,它们与精卵识别、结合以及质膜融合等受精活动密切相关,同时,作为精子膜抗原,在免疫避孕和免疫不育的治疗中具有广阔的应用前景。本文扼要概述了精子膜蛋白的研究进展。     

Molecular models for mouse sperm-oocyte binding

Binding of sperm to egg in the mouse has been proposed to depend primarily on interactions between lectin-like egg-binding proteins on the sperm plasma membrane and complementary carbohydrates on the specialized extracellular matrix of the egg known as the zona pellucida. An alternative model posits that initial sperm-egg binding depends on the interaction of a sperm surface protein with a supramolecular complex of the three mouse zona pellucida glycoproteins (mZP1, mZP2, mZP3); the role of carbohydrate recognition in this paradigm is thought to be minimal (Gahlay G, Gauthier L, Baibakov B, Epifano O,Dean J. 2010. Gamete recognition in mice depends on the cleavage status of an egg's zona pellucida protein. Science.329:216-219). This perspective reviews these recent findings,and considers them in light of evidence favoring a major role for lectin-like interactions. An alternative model, the domain specific model for mammalian gamete binding, could reconcile some of the conflicting observations.     

Pentraxin family of proteins interact specifically with phosphorylcholine and/or phosphorylethanolamine.

Pentraxins are a family of serum proteins characterized by five identical subunits that are noncovalently linked. The two major types of pentraxins are C-reactive protein (CRP) and serum amyloid P component (SAP). CRP proteins are identified by their calcium-dependent interaction with phosphorylcholine. This study showed that SAP also bound to phosphorylated compounds but had a high specificity for phosphorylethanolamine. Thus, human CRP and SAP show high specificity that is complementary for the related compounds, phosphorylcholine and phosphorylethanolamine, respectively. This relationship suggests a complementary and/or related function for the pentraxins. Pentraxins from other species were also examined. Mouse SAP showed binding interactions and specificity similar to human SAP. Female protein (FP) from hamster and rat CRP showed a hybrid specificity and bound to both phosphorylethanolamine and phosphorylcholine. All of the proteins that bound phosphorylethanolamine also associated with human C4b-binding protein (C4BP). With the exception of human and rat CRP, all the proteins also bound to vesicles containing acidic phospholipids. All of these binding interactions were calcium-dependent and mutually exclusive, suggesting that they involved the same site on the protein. These findings suggest possible ways to examine the function of the pentraxins.     

Syndecan-1 and -4 synthesized simultaneously by mouse mammary gland epithelial cells bear heparan sulfate chains that are apparently structurally indistinguishable

Many of the biological functions attributed to cell surface heparan sulfate (HS) proteoglycans, including the Syndecan family, are elicited through the interaction of their HS chains with soluble extracellular molecules. Tightly controlled, cell-specific sulfation and epimerization of HS precursors endows these chains with highly sulfated, iduronate-rich regions, which are major determinants of cytokine and matrix-protein binding and which are interspersed by N-acetylated, poorly sulfated regions. Until this study, there have been no comprehensive structural comparisons made on HS chains decorating simultaneously expressed, but different, syndecan core proteins. In this paper we demonstrate that the HS chains on affinity-purified syndecan-1 and -4 from murine mammary gland cells are essentially identical by a number of parameters. Size determination, disaccharide analyses, enzymatic and chemical scission methods, and affinity co-electrophoresis all failed to reveal any significant differences in fine structure, domain organization, or ligand-binding properties of these HS species. These findings lead us to suggest that the imposition of the fine structure onto HS occurs independently of the core protein to which it is attached and that these core proteins, in addition to the HS chains, may play a pivotal role in the various biological functions ascribed to these macromolecules.