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At least 19 recordsLinked to original sources
PubMed2002

Cleavage of polycystin-1 requires the receptor for egg jelly domain and is disrupted by human autosomal-dominant polycystic kidney disease 1-associated mutations.

Polycystin-1 plays an essential role in renal tubular morphogenesis, and disruption of its function causes cystogenesis in human autosomal-dominant polycystic kidney disease (ADPKD). We demonstrated that polycystin-1 undergoes cleavage at G protein coupled receptor proteolytic site in a process that requires the receptor for egg jelly domain. Most of the N-terminal fragment remains tethered at the cell surface, although a small amount is secreted. PKD1-associated mutations in the receptor for egg jelly domain disrupt cleavage, abolish the ability of polycystin-1 to activate signal transducer and activator of transcription-1, and induce tubulogenesis in vitro. We conclude that the cleavage of polycystin-1 is likely essential for its biologic activity.

Amino Acid Sequence↗
PubMed1999

Identification of a human homologue of the sea urchin receptor for egg jelly: a polycystic kidney disease-like protein.

Previous studies have shown sequence similarity between a region of the autosomal dominant polycystic kidney disease (ADPKD) protein, polycystin-1 and a sea urchin sperm glycoprotein involved in fertilization, the receptor for egg jelly (suREJ). We have analysed sequence databases for novel genes encoding PKD/REJ-like proteins and found a significant region of homology to a large open reading frame in genomic sequence from human chromosome 22. Northern analysis showed that this is a functional gene [termed the polycystic kidney disease and receptor for egg jelly related gene ( PKDREJ )], but unlike polycystin-1, has a very restricted expression pattern; the approximately 8 kb transcript was found exclusively in testis, coincident with the timing of sperm maturation. The PKDREJ transcript was cloned by screening a testis cDNA library and RT-PCR which revealed a 7660 bp mRNA terminating with a 900 bp 3'UTR and a polyA tail. Comparison with genomic sequence showed that PKDREJ is intronless; sequencing the mouse orthologue revealed a similar structure. The predicted human PKDREJ protein has 2253 amino acids (calculated molecular mass 255 kDa) and sequence similarity over approximately 2000 amino acids with polycystin-1, corresponding to the predicted membrane associated region and the area of homology ( approximately 1000 amino acids) with the suREJ protein (the REJ module). The suREJ protein binds the glycoprotein coat of the egg (egg jelly), triggering the acrosome reaction, which transforms the sperm into a fusogenic cell. The sequence similarity and expression pattern suggests that PKDREJ is a mammalian equivalent of the suREJ protein and therefore may have a central role in human fertilization.

Amino Acid Sequence↗
PubMed1998

Acrosome reaction inactivation in sea urchin sperm.

Acrosome reaction inactivation (ARI) is a process that renders sperm irreversibly refractory to the egg jelly (the natural inducer of the acrosome reaction, AR). This process triggered by the egg jelly, is associated with an increase in [Ca2+]i. However, we show here that a rise in [Ca2+]i alone is not sufficient to induce ARI, since artificially increasing [Ca2+]i with either an ionophore or rising external pH, does not trigger ARI. Contrary to the AR which strictly requires Ca2+, ARI can be triggered almost equally well by Sr2+. On the other hand, Mn2+ inhibits ARI and, as we showed earlier, does not affect AR. These observations indicate that the mechanisms involved in ARI differ from those leading to AR. In addition, we report here that high external pH (a non-physiological inducer of AR) triggers the AR in previously inactivated sperm by opening the same Ca2+ channels activated by the egg jelly. Considering that the opening of Ca2+ channels is one of the earliest responses triggered by the egg jelly and that ARI requires the egg jelly receptor to be activated, we have concluded that ARI involves the uncoupling between the egg jelly receptor and Ca2+ channels. Furthermore, intracellular pH (pHi) determinations, in the presence or absence of ionomycin to substitute for the uncoupled Ca2+ channels, indicate that pHi regulation is also impaired in inactivated sperm. In conclusion, ARI is a manifestation of the uncoupling of the egg jelly receptor from the different ion transport systems required for the acrosome reaction.

Acrosome↗
PubMed2004

A third sea urchin sperm receptor for egg jelly module protein, suREJ2, concentrates in the plasma membrane over the sperm mitochondrion.

Sea urchin spermatozoa are model cells for studying signal transduction events underlying flagellar motility and the acrosome reaction. We previously described the sea urchin sperm receptor for egg jelly 1 (suREJ1) which consists of 1450 amino acids, has one transmembrane segment and binds to the fucose sulfate polymer of egg jelly to induce the sperm acrosome reaction. We also cloned suREJ3 which consists of 2681 amino acids and has 11 putative transmembrane segments. Both these proteins localize to the plasma membrane over the acrosomal vesicle. While cloning suREJ1, we found suREJ2, which consists of 1472 amino acids, has two transmembrane segments and is present in the entire sperm plasma membrane, but is concentrated over the sperm mitochondrion. Experimental evidence suggests that, unlike suREJ1 and suREJ3, suREJ2 does not project extracellularly from the plasma membrane, but is an intracellular plasma membrane protein. All three sea urchin sperm REJ proteins possess a protein module of > 900 amino acids, termed 'the REJ module', that is shared by the human autosomal dominant polycystic kidney disease protein, polycystin-1, and PKDREJ, a testis-specific protein in mammals whose function is unknown. In the present study, we describe the sequence, domain structure and localization of suREJ2 and speculate on its possible function.

Amino Acid Sequence↗
PubMed2004

Positive selection in the carbohydrate recognition domains of sea urchin sperm receptor for egg jelly (suREJ) proteins.

A wealth of evidence shows that protein-carbohydrate recognition mediates the steps of gamete interaction during fertilization. Carbohydrate-recognition domains (CRDs) comprise a large family of ancient protein modules of approximately 120 amino acids, having the same protein fold, that bind terminal sugar residues on glycoproteins and polysaccharides. Sea urchin sperm express three suREJ (sea urchin receptor for egg jelly) proteins on their plasma membranes. suREJ1 has two CRDs, whereas suREJ2 and suREJ3 both have one CRD. suREJ1 binds the fucose sulfate polymer (FSP) of egg jelly to induce the sperm acrosome reaction. The structure of FSP is species specific. Therefore, the suREJ1 CRDs could encode molecular recognition between sperm and egg underlying the species-specific induction of the acrosome reaction. The functions of suREJ2 and suREJ3 have not been explored, but suREJ3 is exclusively localized on the plasma membrane over the sperm acrosomal vesicle and is physically associated with sea urchin polycystin-2, a known cation channel. An evolutionary analysis of these four CRDs was performed for six sea urchin species. Phylogenetic analysis shows that these CRDs were already differentiated in the common ancestor of these six sea urchins. The CRD phylogeny agrees with previous work on these species based on one nuclear gene and several mitochondrial genes. Maximum likelihood shows that positive selection acts on these four CRDs. Threading the suREJ CRDs onto the prototypic CRD crystal structure shows that many of the sites under positive selection are on extended loops, which are involved in saccharide binding. This is the first demonstration of positive selection in CRDs and is another example of positive selection acting on the evolution of gamete-recognition proteins.

Animals↗
PubMed2006

Polycystic kidney disease and receptor for egg jelly is a plasma membrane protein of mouse sperm head.

The mammalian polycystic kidney disease (PKD) gene family comprises eight members whose role in cell physiology is still poorly understood. Two of the founding members of the PKD family, PKD1 and PKD2, are responsible for the majority of cases of autosomal dominant polycystic kidney disease. The present study focuses on a PKD1 homologue, mouse polycystic kidney disease and receptor for egg jelly (PKDREJ) and its putative role in mammalian fertilization. To examine PKDREJ tissue distribution multiple-tissue Northern blot analysis was performed. We observed that PKDREJ expression is confined to mouse testis. A PKDREJ transcript was detected in spermatogenic cells by in situ hybridization with mouse testicular tissue. Upon heterologous expression PKDREJ was retained in intracellular membrane compartments and unlike PKD1 did not undergo cleavage in the G-protein-coupled receptor proteolytic site domain (GPS). Immunocytochemical experiments on isolated epididymal mouse spermatozoa using PKDREJ-specific polyclonal antibodies revealed that the protein is localized in the acrosomal region and on the inner aspect of the falciform-shaped head. To precisely characterize PKDREJ expression in the acrosomal region, transmission electron microscopy was performed. Immunogold labeling was only visible at the plasma membrane of the mouse sperm head. Collectively, these data suggest PKDREJ to be a sperm plasma membrane protein presumably contributing to transmembrane signaling in mammalian spermatozoa.

Animals↗
PubMed1996

The sea urchin sperm receptor for egg jelly is a modular protein with extensive homology to the human polycystic kidney disease protein, PKD1.

During fertilization, the sea urchin sperm acrosome reaction (AR), an ion channel-regulated event, is triggered by glycoproteins in egg jelly (EJ). A 210-kD sperm membrane glycoprotein is the receptor for EJ (REJ). This conclusion is based on the following data: purified REJ binds species specifically to EJ dotted onto nitrocellulose, an mAb to REJ induces the sperm AR, antibody induction is blocked by purified REJ, and purified REJ absorbs the AR-inducing activity of EJ. Overlapping fragments of REJ cDNA were cloned (total length, 5,596 bp). The sequence was confirmed by microsequencing six peptides of mature REJ and by Western blotting with antibody to a synthetic peptide designed from the sequence. Complete deglycosylation of REJ followed by Western blotting yielded a size estimate in agreement with that of the mature amino acid sequence. REJ is modular in design; it contains one EGF module and two C-type lectin carbohydrate-recognition modules. Most importantly, it contains a novel module, herein named the REJ module (700 residues), which shares extensive homology with the human polycystic kidney disease protein (PKD1). Mutations in PKD1 cause autosomal dominant polycystic kidney disease, one of the most frequent genetic disease of humans. The lesion in cellular physiology resulting from mutations in the PKD1 protein remains unknown. The homology between REJ modules of the sea urchin REJ and human PKD1 suggests that PKD1 could be involved in ionic regulation.

Amino Acid Sequence↗
PubMed1989

Evidence for the activation of two different Ca2+ channels during the egg jelly-induced acrosome reaction of sea urchin sperm.

The influx of Ca2+ and its subsequent intracellular increase are required for the acrosome reaction of sea urchin sperm to occur. Spermatozoa must undergo this reaction, which is triggered by the egg jelly, in order to fertilize the egg. Here, the egg jelly-induced Ca2+ influx mechanisms have been studied in sperm loaded with FURA-2 using Mn2+ under the assumption that this divalent ion is an indicator of Ca2+ influx through Ca2+ channels. Egg jelly induced the immediate entry of Ca2+ (mixing time 1 s), however; we found that the influx of Mn2+ increased after a lag time of 5 s. Nisol-dipine (a Ca2+ channel blocker) did not block the Mn2+ influx which was inhibited by 40 mM of external [K+], low Na+, and 5 mM of tetraethylammonium (a K+ channel blocker). These conditions also inhibited the alkalinization and the acrosome reaction. The inhibition of the Mn2+ influx could be overcome by increasing internal pH (pHi) with ammonium (10 mM). On the contrary the influx of Ca2+ during the first 5 s was not inhibited by any of the conditions indicated before, except by nisoldipine. These data could be explained by the activation of two different Ca2+ channels by egg jelly. The first one being a receptor-operator Ca2+ channel that opens when the receptor for egg jelly is occupied independently of the ionic conditions. The other one could be considered as a second messenger-operated Ca2+ channel that requires at least an increase in pHi to open.

Acrosome↗
PubMed2004

Polycystin-1L2 is a novel G-protein-binding protein.

Mutations in genes encoding polycystin-1 (PC1) and polycystin-2 cause autosomal dominant polycystic kidney disease. The polycystin protein family is composed of Ca2+-permeable pore-forming subunits and receptor-like integral membrane proteins. Here we describe a novel member of the polycystin-1-like subfamily, polycystin-1L2 (PC1L2), encoded by PKD1L2, which has various alternative splicing forms with two translation initiation sites. PC1L2 short form starts in exon 12 of the long form. The longest open reading frame of PKD1L2 short form, determined from human testis cDNA, encodes a 1775-amino-acid protein and 32 exons, whereas the long form is predicted to encode a 2460-residue protein. Both forms have a small receptor for egg jelly domain, a G-protein-coupled receptor proteolytic site, an LH2/PLAT, and 11 putative transmembrane domains, as well as a number of rhodopsin-like G-protein-coupled receptor signatures. RT-PCR analysis shows that the short form, but not the long form, of human PKD1L2 is expressed in the developing and adult heart and kidney. Furthermore, by GST pull-down assay we observed that PC1L2 and polycystin-1L1 are able to bind to specific G-protein subunits. We also show that PC1 C-terminal cytosolic domain binds to Galpha12, Galphas, and Galphai1, while it weakly interacts with Galphai2. Our results indicate that both PC1-like molecules may act as G-protein-coupled receptors.

Alternative Splicing↗
PubMed2026

Genomic and Structural Analysis of Gamete Recognition Proteins in a Broadcast Spawning Echinoderm Mesocentrotus franciscanus.

Gamete recognition proteins are expressed on the surfaces of sperm and eggs, where they mediate interactions between gametes. The genetic basis for gamete recognition proteins, as well as their structure and interactions, have yet to be fully resolved. Using a new high-quality de novo genome assembly for the sea urchin Mesocentrotus franciscanus, we investigated the genomic structure, expression, and protein forms of several gamete recognition proteins: sperm bindin, egg receptor for sperm (HSP110), and egg bindin receptor (EBR1), as well as the receptor for egg jelly (REJ) and its paralogs. To inform future population genetic and evolutionary studies, we resolve the genomic structure of the large EBR1 protein, identifying fewer tandem CUB-TSP1 repeats in EBR1 compared to the initial characterization of this protein. As expected for an egg receptor for sperm, EBR1 is highly expressed in female reproductive tissues (eggs and female gonad), compared to other tissues. In contrast, HSP110 shows similar levels of expression across male and female reproductive tissues, as well as across non-reproductive tissues and development stages. HSP110 might be a pleiotropic gene that in part influences fertilization. Using protein structural modeling and functional domain predictions, we propose hypotheses about potential interactions among EBR1, bindin, and HSP110 proteins that may provide insight into sperm-egg interactions in sea urchins. Resolving the genomic structure of genes encoding gamete recognition proteins, in combination with functional annotations and protein structural modeling, enables deeper investigation into the consequences of variation in gamete recognition proteins and the evolution of reproductive isolation.

Mesocentrotus franciscanus↗
PubMed2001

suREJ3, a polycystin-1 protein, is cleaved at the GPS domain and localizes to the acrosomal region of sea urchin sperm.

The sea urchin sperm acrosome reaction (AR) is a prerequisite for sperm-egg fusion. This report identifies sea urchin sperm receptor for egg jelly-3 (suREJ3) as a new member of the polycystin-1 family (the protein mutated in autosomal dominant polycystic kidney disease). suREJ3 is a multidomain, 2,681-amino acid, heavily glycosylated orphan receptor with 11 putative transmembrane segments (TMS) that localize to the plasma membrane covering the sperm acrosomal vesicle. Like the latrophilins and other members of the secretin family of G-protein-coupled receptors, suREJ3 is cleaved at the consensus GPS (G-protein-coupled receptor proteolytic site) domain. Antibodies to the extracellular 1,455-residue NH(2)-terminal portion identify a band at 250 kDa that shifts in electrophoretic mobility to 180 kDa upon glycosidase digestion. Antibodies to the 1,226-residue COOH-terminal portion identify a band at 150 kDa that shifts to 140 kDa after glycosidase treatment. Antibodies to both portions of suREJ3 localize exclusively to the plasma membrane over the acrosomal vesicle. Immunoprecipitation shows that both portions of suREJ3 are associated in detergent extracts. This is the first report showing that a polycystin family member is cleaved at the GPS domain. Localization of suREJ3 to the acrosomal region provides the first suggestion for the role of a polycystin-1 protein (components of nonselective cation channels) in a specific cellular process.

Acrosome↗
PubMed1997

The fucose sulfate polymer of egg jelly binds to sperm REJ and is the inducer of the sea urchin sperm acrosome reaction.

The sea urchin sperm cell is an advantageous model for studying ligand-mediated exocytosis. Sperm can be obtained in vast quantities and induced to undergo exocytosis of the acrosomal vesicle with great synchrony. During sea urchin fertilization, egg jelly (EJ) triggers the sperm acrosome reaction (AR) which is required for sperm binding and fusion with the egg. Uncertainty exists as to the exact biochemical nature of the AR inducer. The following study was performed in an attempt to clarify the nature of the inducer. EJ from individual females (Strongylocentrotus purpuratus) was analyzed on SDS-PAGE gels. Each female had a unique composition of EJ macromolecules, but all females possessed the previously described fucose sulfate polymer (FSP). Two electrophoretic isotypes of FSP were discovered; 87% of females had only one isotype and 13% had both. Both FSP isotypes bound to the REJ protein (receptor for egg jelly) purified from sperm. The two FSP isotypes had almost equal potency in inducing the AR. EJ was fractionated by DEAE chromatography in 6 M urea/4% beta-mercaptoethanol. All AR-inducing activity coeluted with FSP. FSP, purified by trypsin digestion followed by dialysis, was twice as active as the non-trypsin-digested control at inducing the AR. EJ was digested with proteinase K, boiled in detergent and beta-mercaptoethanol, and subjected to sucrose density gradient sedimentation. The FSP and AR activity had superimposable sedimentation patterns. Purified FSP had no associated peptide component. Sperm from individual males differed in the concentration dependency of purified FSP to induce the AR. The data indicate that the 138/82 kDa EJ glycoproteins, previously thought to act as AR inducers, do not appear to be involved in triggering the AR. The data are consistent with the hypothesis that FSP is the only inducer of the AR of this sea urchin species.

Acrosome↗
PubMed1993

A GPI-anchored sea urchin sperm membrane protein containing EGF domains is related to human uromodulin.

An Mr 63-kD sea urchin sperm flagellar membrane protein has been previously implicated as a possible receptor for egg jelly ligand(s) that trigger the sperm acrosome reaction (AR). The cDNA and deduced amino acid sequences of the 63-kD protein are presented. The open reading frame codes for a protein of 470 amino acids which contains a putative signal sequence of 25 residues. Western blots using antibodies to two synthetic peptides confirm the sequence to be that of the 63-kD protein. The mRNA is approximately 2,300 bases in length and the gene appears to be single copy. The protein is released from sperm membrane vesicles by treatment with phosphatidylinositol-specific phospholipase C, showing that it is anchored to the flagellar membrane by glycosylphosphatidyl inositol (GPI). Although we cannot demonstrate involvement of the 63-kD protein in the AR, it is of potential interest because it shares significant similarity with the developmentally expressed proteins crumbs, notch and xotch as well as human uromodulin over a region that includes two separate EGF repeats.

Amino Acid Sequence↗
PubMed1998

Sperm-egg binding in the sea urchin: a high level of intracellular ATP stabilizes sperm attachment to the egg receptor.

Previous studies have established that a recombinant protein fragment (45A) of the egg receptor for sperm of the sea urchin Strongylocentrotus purpuratus exhibits several characteristics that are consistent with that expected of a receptor. Using a quantitative sperm binding assay with glutathione S-transferase fused to a recombinant protein containing the C-terminal half of the 45A construct immobilized on glutathione beads, it was found that the interaction between sperm and this protein is a kinetically transient event. Sperm binding to the receptor fragment reached a maximum at 20 s after adding sperm in the presence of egg jelly to beads coated with recombinant receptor. In the next 20-120 s, approximately 50-70% of the sperm detached from the beads. Similar phenomena were observed when the kinetics of sperm binding to dejellied, glutaraldehyde-fixed eggs were studied. Because the acrosome reaction, a prelude to binding, is known to be accompanied by a decrease in the ATP level of sperm, we studied the effect of various inhibitors on both sperm detachment and the level of ATP. It was found that the detachment rate increased slightly when respiration inhibitors that blocked ATP production in mitochondria were added. In contrast, the dynein ATPase inhibitor, erythro-9-[3-hydroxynonyl]adenine, which is known to inhibit flagellum motility by blocking ATP utilization, stabilized the binding of sperm to the receptor and allowed maintenance of a high internal ATP level. Immotile, tailless sperm that physically lacked dynein ATPase, and therefore sustained their internal ATP levels, also exhibited stable binding provided that the sperm and beads were physically mixed. These results suggest that the internal ATP level of the sperm controls the stability of its binding to the receptor. The possible mechanism of the detachment and its significance with respect to the overall process of fertilization are discussed.

Adenine↗
PubMed2000

A 130-kDa membrane protein of sperm flagella is the receptor for asterosaps, sperm-activating peptides of starfish Asterias amurensis.

Spermatozoa of the starfish, Asterias amurensis, have a specific receptor for asterosap, a sperm-activating peptide isolated from the jelly coat of homologous eggs. We characterized the receptor by using several asterosap derivatives. Analysis of equilibrium binding of radioactive di-iodinated Bolton-Hunter reagent-labeled asterosap ((125)I(2)-BHP15) to the spermatozoa indicated that the cell has 1.1 x 10(5) binding sites of high affinity (K(d) = 57 pM), and also the receptor showed positive cooperativity for asterosap binding. When spermatozoa were treated with fluorophore-labeled asterosap, the sperm flagella were labeled, indicating that the receptors are mostly localized in the sperm tail. When spermatozoa were reacted with radioactive asterosap prelabeled with photoaffinity cross-linkers, a single 130-kDa membrane protein of sperm flagella was specifically radiolabeled. This result was reproducible regardless of the length of spacer arm of cross-linkers so far studied. Therefore, the 130-kDa protein is likely to be the receptor for asterosaps. Modification of asterosap at the N-terminal region with bulky molecules such as carboxyfluorescein did not affect the activity of asterosap, suggesting that the N-terminus of asterosap is not involved in the ligand-receptor interaction. On the other hand, S-alkylated asterosaps did not compete with (125)I(2)-BHP15 for binding to the receptor, indicating that disulfide linkage of asterosap is essential for the ligand-receptor interaction. The properties of the receptor, high affinity and high concentration, enabled us to apply the fluorescence polarization technique to study the molecular interaction between asterosap and the receptor. Using this method, we performed binding experiments in almost real time and found that divalent cations are significantly involved in the interaction between asterosap and the receptor.

Affinity Labels↗
PubMed1982

Isolation of an arbacia sperm fertilization antigen.

Antisperm antibody fragments (IFab) block sea urchin fertilization by inhibiting the acrosome reaction and consequently sperm-egg attachment. We describe here a 68,000 dalton MW glycoprotein which neutralizes the fertilization-inhibiting action of IFab. This glycoprotein is a minor component is SDS-polyacrylamide gels of sperm membranes, but is greatly enriched in lithium diiodosalicylate extracts of the membranes. Final purification of the antigen was accomplished by elution from preparative SDS-polyacrylamide gels. This glycoprotein is evidently the sea urchin sperm receptor which interacts wih the egg jelly coat and acts as a "trigger" for the acrosome reaction.

Animals↗
PubMed1994

Speract receptors are localized on sea urchin sperm flagella using a fluorescent peptide analog.

In two species of sea urchins, Strongylocentrotus purpuratus and Lytechinus pictus, the egg jelly-associated decapeptide, speract, binds to specific sperm surface receptors resulting in increased sperm motility and respiration rate. Previously, a peptide analog, GGG[Y2]-speract, was used to identify a 77-kDa receptor on intact sperm cells using chemical cross-linking. In this paper we describe the synthesis and characterization of a fluorescent derivative of GGG[Y2]-speract for use as a probe for the sperm receptor. Fluorescein isothiocyanate (FITC) was conjugated to the amino terminus of GGG[Y2]-speract and the resulting analog (FITC-GGG[Y2]-speract) was purified by size exclusion chromatography and reverse-phase HPLC. Competition binding studies with the fluorescent peptide and intact spermatozoa yielded IC50 values which were indistinguishable from native speract and GGG[Y2]-speract (approximately 20 nM). FITC-GGG[Y2]-speract half-maximally stimulated sperm respiration at a concentration nearly identical to that of the native peptide (EC50 approximately 50 pM). Using digitally enhanced video imaging fluorescence microscopy, FITC-GGG[Y2]-speract was used to localize the speract receptor on the flagella of intact sperm. Excess concentrations of both unlabeled speract and GGG[Y2]-speract abolished the binding of the fluorescent analog, yet unrelated peptides did not. Further, results of cross-linking experiments using 125I-GGG[Y2]-speract and purified sperm flagella and heads were consistent with the fluorescent labeling results on whole cells. The finding that the speract receptor is localized exclusively to the sperm flagella may reveal its role in the regulation of flagellar motility.

Amino Acid Sequence↗
PubMed1986

Phosphorylation of sperm histone H1 is induced by the egg jelly layer in the sea urchin Strongylocentrotus purpuratus.

Phosphorylation of histone H1 occurs when spermatozoa of the sea urchin Strongylocentrotus purpuratus are treated with the macromolecular fraction of solubilized egg jelly. Phosphorylation is on serine residues in the N-terminal fragment of H1 bisected with N-bromosuccinimide. Phosphorylation is maximal by 4-8 min and dependent on Ca2+, but independent of Na+ or increased intracellular pH. Phosphorylation of H1 can be dissociated from the induction of the acrosome reaction. Only a fraction of the H1 molecules become phosphorylated upon treatment of sperm with egg jelly. The amount of phosphate per mole of H1 increases from 0.15 moles before jelly treatment to 0.46 moles after maximal phosphorylation. Phosphorylation of H1 occurs in a cAMP-dependent manner as indicated by the ability of the phosphodiesterase inhibitors IBMX and SQ20009 to induce H1 phosphorylation. This phosphorylation reaction can be blocked by digesting the sperm surface with Pronase, or preincubation of sperm in wheat germ agglutinin, showing that a ligand in egg jelly must interact with a sperm surface receptor to activate the kinase phosphorylating H1.

1-Methyl-3-isobutylxanthine↗