Sperm Acrosin

Limited proteolysis by acrosin affects sperm-binding and mechanical resilience of the mouse zona pellucida

The encounter of oocyte and sperm is the key event initiating embryonic development in mammals. Crucial functions of this existential interaction are determined by proteolytic enzymes, such as acrosin, carried in the sperm head acrosome, and ovastacin, stored in the oocyte cortical granules. Ovastacin is released upon fertilisation to cleave the zona pellucida, a glycoprotein matrix surrounding the oocyte. This limited proteolysis hardens the oocyte envelope, and thereby provides a definitive block against polyspermy and protects the developing embryo. On the other hand, acrosin, the renowned and most abundant acrosomal protease, has been thought to enable sperm to penetrate the oocyte envelope. Depending on the species, proteolytic cleavage of the zona pellucida by acrosin is either essential or conducive for fertilisation. However, the specific target cleavage sites and the resulting physiological consequences of this proteolysis remained obscure. Here, we treated native mouse zonae pellucidae with active acrosin and identified two cleavage sites in zona pellucida protein 1 (ZP1), five in ZP2 and one in ZP3 by mass spectrometry. Several of these sites are highly conserved in mammals. Remarkably, limited proteolysis by acrosin leads to zona pellucida remodelling rather than degradation. Thus, acrosin affects both sperm binding and mechanical resilience of the zona pellucida, as assessed by microscopy and nanoindentation measurements, respectively. Furthermore, we ascertained potential regulatory effects of acrosin, via activation of latent pro-ovastacin and inactivation of fetuin-B, a tight binding inhibitor of ovastacin. These results offer novel insights into the complex proteolytic network modifying the extracellular matrix of the mouse oocyte, which might apply also to other species.

Improved preimplantation development of bovine ICSI embryos generated with spermatozoa pretreated with membrane-destabilizing agents lysolecithin and Triton X-100

In cattle, intracytoplasmic sperm injection (ICSI) has a low efficiency. The acrosome content may be responsible for this effect because of the large amount of hydrolytic enzymes that are released within the oocyte. With the aim of removing the acrosome and destabilize the membranes, cryopreserved bovine spermatozoa were treated with lysolecithin (LL) and Triton X-100 (TX) at different concentrations. We evaluated the membrane integrity, the acrosome integrity, DNA integrity, and the variation of phospholipase C zeta. The rates of development (cleavage and blastocysts) were also evaluated along with pronuclear formation and the embryo quality. Spermatozoa incubated with LL and TX (0.01%, 0.02%, 0.03%, and 0.04%) decreased (P < 0.0001) sperm viability in a dose-dependent manner. The acrosome reaction was also increased (P < 0.0001) in all tested concentrations of LL and TX achieving 100% at 0.05% concentration in both treatments. Terminal deoxynucleotidyl transferase dUTP nick-end labeling assay reported an increase (P < 0.05) in DNA fragmentation only with the highest concentration of LL (0.06%), whereas all concentrations assessed of TX reported an increased respect to the control. Phospholipase C zeta expression decreased (P < 0.05) in spermatozoa treated with LL and TX at all concentrations tested. A higher cleavage rate was observed in ICSI-TX (66%) and ICSI-LL (65%) groups compared with the untreated control group (51%) and the blastocyst formation rate significantly increased in the ICSI-LL group (29%) compared with the control (21%). No differences were observed in the pronuclear formation and quality of the embryos. In conclusion, the destabilization of the plasma membrane and the release of the acrosomal content with LL and TX before ICSI improve the rate of embryonic development, without affecting the quality of the embryos produced by this technique.

Sperm proteases and extracellular ubiquitin-proteasome system involved in fertilization of ascidians and sea urchins

Ascidians (primitive chordates) are hermaphroditic animals that release spermatozoa and eggs almost simultaneously, but some species, including Halocynthia roretzi, show strict self-sterility. In H. roretzi, a 70-kDa vitelline coat (VC) protein consisting of 12 EGF-like repeats, named HrVC70, appears to be a promising candidate for the self/nonself-recognition (or allorecognition) system during gamete interaction. After spermatozoon recognizes the VC as nonself, sperm 700-kDa extracellular ubiquitin-conjugating enzyme complex appears to ubiquitinate Lys234 of HrVC70, and the ubiquitinated HrVC70 is degraded by the sperm 26S proteasome that is located on the sperm head surface. This novel ubiquitin-proteasome system enables spermatozoa to penetrate through the VC. Sperm trypsin-like proteases, acrosin and spermosin, also participate in fertilization, probably as sperm-side 'movable' binding proteins to the VC.

Larval release in brachyuran crustaceans Functional similarity of peptide pheromone receptor and catalytic site of trypsin

Studies of crab egg hatching and larval release behavior in the crab,Rhithropanopeus harrisii, generated a model describing the process. In the model, carboxyl terminal arginine peptides serve as pheromones that synchronize larval release. In response to the peptides, the female performs Stereotypic larval release behavior and casts larvae into the water column. The peptides originate from trypsin-like enzymatic activity as part of the egghatching process. Hatching can be simulated experimentally by incubating ovigerous crabs in either bovine or porcine trypsin. The female performs the larval release behavior. Eggs detach from the female, and immobile larvae hatch prematurely. Preincubation of trypsin with trypsin inhibitors eliminates these effects. Approximately nanomolar concentrations of five different polypeptide trypsin inhibitors evoke the female's larval release behavior. Because both peptides and trypsin inhibitors evoke larval release behavior and because trypsin inhibitors bind to both the peptide receptor and the enzyme with high affinity, the receptor binding site and trypsin catalytic site must be very similar. A relationship between the binding site of a peptide receptor and the catalytic site of trypsin is postulated. The difference may be substitution by a basic amino acid for the catalytic site serine. Molecular graphics modeling indicates that all necessary conditions for receptor binding can be met by substitution with lysine for the active site serine in the trypsin catalytic site. This substitution eliminates catalytic activity, maintains the binding affinity for trypsin inhibitors, and increases binding strength for peptides.

Ascidian sperm lysin system

Fertilization is a precisely controlled process involving many gamete molecules in sperm binding to and penetration through the extracellular matrix of the egg. After sperm bind to the extracellular matrix (vitelline coat), they undergo the acrosome reaction which exposes and partially releases a lytic agent called "lysin" to digest the vitelline coat for the sperm penetration. The vitelline coat sperm lysin is generally a protease in deuterostomes. The molecular mechanism of the actual degradation of the vitelline coat, however, remains poorly understood. In order to understand the lysin system, we have been studying the fertilization mechanism in ascidians (Urochordata) because we can obtain large quantities of gametes which are readily fertilized in the laboratory. Whereas ascidians are hermaphrodites, which release sperm and eggs simultaneously, many ascidians, including Halocynthia roretzi, are strictly self-sterile. Therefore, after sperm recognize the vitelline coat as nonself, the sperm lysin system is thought to be activated. We revealed that two sperm trypsin-like proteases, acrosin and spermosin, the latter of which is a novel sperm protease with thrombin-like substrate specificity, are essential for fertilization in H. roretzi. These molecules contain motifs involved in binding to the vitelline coat. We found that the proteasome rather than trypsin-like proteases has a direct lytic activity toward the vitelline coat. The target for the ascidian lysin was found to be a 70-kDa vitelline coat component called HrVC70, which is made up of 12 EGF-like repeats. In addition to the proteasome system, the ubiquitination system toward the HrVC70 was found to be necessary for ascidian fertilization. In this review, I describe recent progress on the structures and roles in fertilization of the two trypsin-like proteases, acrosin and spermosin, and also on the novel extracellular ubiquitin-proteasome system, which plays an essential role in the degradation of the ascidian vitelline coat.

Spermosin, a trypsin-like protease from ascidian sperm: cDNA cloning, protein structures and functional analysis

We have previously reported that two trypsin-like enzymes, acrosin and spermosin, play key roles in sperm penetration through the vitelline coat of the ascidian (Urochordata) Halocynthia roretzi [Sawada et al. (1984), J. Biol. Chem. 259, 2900-2904; Sawada et al. (1984), Dev. Biol. 105, 246-249]. Here, we show the amino-acid sequence of the ascidian preprospermosin, which is deduced from the nucleotide sequence of the isolated cDNA clone. The isolated ascidian preprospermosin cDNA consisted of 1740 nucleotides, and an open reading frame encoding 388 amino acids, which corresponds to a molecular mass of 41 896 Da. By sequence alignment, it was suggested that His178, Asp230 and Ser324 make up a catalytic triad and that ascidian spermosin be classified as a novel trypsin family member. The mRNA of preprospermosin is specifically expressed in ascidian gonads but not in other tissues. Purified spermosin consists of 33- and 40-kDa bands as determined by SDS/PAGE under nonreducing conditions. The 40-kDa spermosin consists of a heavy chain (residues 130-388) and a long light chain designated L1 (residues 23-129), whereas the 33-kDa spermosin includes the same heavy chain and a shorter light chain designated L2 (residues 97-129). The L1 chain contains a proline-rich region, designated L1(DeltaL2) which is lacking in L2. Investigation with the glutathione-S-transferase (GST)-spermosin-light-chain fusion proteins, including GST-L1, GST-L2, and GST-L1(DeltaL2), revealed that the proline-rich region in the L1 chain binds to the vitelline coat of ascidian eggs. Thus, we propose that sperm spermosin is a novel trypsin-like protease that binds to the vitelline coat and also plays a part in penetration of sperm through the vitelline coat during ascidian fertilization.

cDNA cloning and functional analysis of ascidian sperm proacrosin

cDNA cloning and functional analysis of proacrosin from the ascidian Halocynthia roretzi were undertaken. The isolated cDNA of the ascidian preproacrosin consists of 2367 nucleotides, and an open reading frame encodes 505 amino acids, which corresponds to the molecular mass of 55,003 Da. The mRNA of proacrosin was found to be specifically expressed in the gonad by Northern blotting and in the spermatocytes or spermatids by in situ hybridization. The amino acid sequences around His(76), Asp(132), and Ser(227), which make up a catalytic triad, showed high homology to those of the trypsin family. Ascidian acrosin has paired basic residues (Lys(56)-His(57)) in the N-terminal region, which is one of the most characteristic features of mammalian acrosin. This region seems to play a key role in the binding of (pro)acrosin to the vitelline coat, because the peptide containing the paired basic residues, but not the peptide substituted with Ala, was capable of binding to the vitelline coat. Unlike mammalian proacrosin, ascidian proacrosin contains two CUB domains in the C-terminal region, in which CUB domain 1 seems to be involved in its binding to the vitelline coat. Four components of the vitelline coat that are capable of binding to CUB domain 1 in proacrosin were identified. In response to sperm activation, acrosin was released from sperm into the surrounding seawater, suggesting that ascidian acrosin plays a key role in sperm penetration through the coat. These results indicate that ascidian sperm contains a mammalian acrosin homologue, a multi-functional protein working in fertilization.

Evidence for the activation of PAR-2 by the sperm protease, acrosin: expression of the receptor on oocytes

Proteinase-activated receptor-2 (PAR-2) is a member of a family of G-protein-coupled, seven-transmembrane domain receptors that are activated by proteolytic cleavage. The receptor is expressed in a number of different tissues and potential physiological activators identified thus far include trypsin and mast cell tryptase. Acrosin, a trypsin-like serine proteinase found in spermatozoa of all mammals, was found to cleave a model peptide fluorescent quenched substrate representing the cleavage site of PAR-2. This substrate was cleaved with kinetics similar to those of the known PAR-2 activators, trypsin and mast cell tryptase. Acrosin was also shown to induce significant intracellular calcium responses in Chinese hamster ovary cells stably expressing intact human PAR-2, most probably due to activation of the receptor. Immunohistochemical studies using PAR-2 specific antibodies indicated that the receptor is expressed by mouse oocytes, which suggests that acrosin may play additional role(s) in the fertilization process via the activation of PAR-2 on oocytes.

Difference of acrosomal serine protease system between mouse and other rodent sperm

A fraction of acrosomal proteins dispersed during calcium ionophore A23187-induced acrosome reaction was prepared from cauda epididymal sperm of wild-type and acrosin-deficient mice, rat, and hamster. The acrosome-reacted sperm were further extracted by Nonidet P-40 to obtain the detergent-soluble protein fraction. Activities of serine proteases in the two protein fractions were examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence of gelatin. A mixture of 42- and 41-kDa gelatin-hydrolyzing proteases was found in both fractions of the wild-type mouse sperm, whereas the acrosin-deficient mouse sperm contained the active 42-kDa protease and apparently lacked the activity of the 41-kDa protease. However, exogenous bovine pancreatic trypsin compensated for the absence of acrosin in the protein fractions of the mutant mouse sperm; the gelatin-hydrolyzing activity of the 41-kDa protease appeared when the sperm proteins of the mutant mice were treated with pancreatic trypsin. Two-dimensional polyacrylamide gel electrophoresis revealed that the 42- and 41-kDa proteases were distinguished from acrosin by the isoelectric point and immunoreactivity with affinity-purified antibody against an oligopeptide corresponding to the N-terminal amino acid sequence of mouse proacrosin. Moreover, the gelatin-hydrolyzing proteins corresponding to these two proteases were not detected in rat and hamster sperm, in spite of the treatment of the sperm extracts with pancreatic trypsin, and the total amount of gelatin-hydrolyzing activities in mouse was much smaller than those in rat and hamster. These results may reflect the difference of the serine protease system for the sperm penetration through the egg zona pellucida between mouse and other rodent animals, possibly explaining why the acrosin-deficient mouse sperm are capable of penetrating the zona pellucida.

Characterization of mouse epididymal acrosin: comparative studies with acrosin from boar and human ejaculated spermatozoa

Acrosin is an acrosomal protease believed to play a major role in fertilization. It is synthesized as an inactive precursor, proacrosin, which is processed via (auto)proteolysis into active form(s). In this paper, comparative studies on the characteristics of acrosin from mouse, boar and human are reported. The mouse proacrosin/acrosin was especially investigated to clarify whether or not the enzyme undergoes modifications during epididymal maturation. Acrosomal extracts from mature and immature mouse spermatozoa, as well as from ejaculated boar and human spermatozoa, were analysed by means of SDS-electrophoresis, Western blot and activity measurements. The studies showed that epididymal maturation produced a shift in the molecular weight of proacrosin. It was also observed that the activation kinetics differ strongly between the three species studied. Human proacrosin showed a constant substrate turnover, acrosin from boar showed sigmoidal activation kinetics and mouse acrosin, either from the caput or the cauda epididymides, showed a rapid decay in activity, suggesting the presence of an endogenous specific inhibitor.

Identification of potential activators of proteinase-activated receptor-2

In order to identify physiological activators of proteinase-activated receptor-2 (PAR-2), a peptide chloromethane inhibitor (biotinyl-Ser-Lys-Gly-Arg-CH2Cl) based on the cleavage site for activation of PAR-2 was synthesised and tested with 12 trypsin-like serine proteinases. The second-order rate constant (ki/Ki) for the formation of the covalent proteinase-inhibitor complex varied by 2 x 10(5)-fold between the proteinases. Biotinyl-Ser-Lys-Gly-Arg-CH2Cl reacted very rapidly with trypsin, acrosin from sperm and tryptase from mast cells: the ki/Ki values with these proteinases were greater than 10(5) M(-1) x s(-1). Thus, the specificity of these proteinases matched the sequence of the activation site of PAR-2 and it can be concluded that these proteinases are potential physiological activators of PAR-2.

Rapid inhibition of the sperm protease acrosin by protein C inhibitor

Heparin was found to be an allosteric modulator of the amidolytic activity of the protease acrosin. In the presence of saturating concentrations of heparin, there was a 4.9-fold decrease in the value of the Michaelis constant for the substrate D-Ile-Pro-Arg-p-nitroanilide and the value of kcat was 2.5-fold lower. Analysis of the data yielded a dissociation constant of 0.22 +/- 0.04 microM for the heparin-acrosin complex. The presence of relatively high concentrations of protein C inhibitor in seminal plasma [Laurell, M., Christensson, A., Abrahamson, P., Stenflo, J., & Lilja, H. (1992) J. Clin. Invest. 89, 1094-1101] suggests that this serpin may be involved in the control of the activity of acrosin. Acrosin was found to be rapidly inhibited by protein C inhibitor with the association rate constant (kass) for the formation of the complex being (2.41 +/- 0.03) x 10(5) M-1 s-1. The value of kass showed a bell-shaped dependence on the concentration of heparin; it was maximal at concentrations of heparin between 0.08 and 3 microM and decreased at lower and higher concentrations. At the optimal heparin concentration, the value of kass for the acrosin-protein C inhibitor reaction was 230-fold higher ((5.6 +/- 0.1) x 10(7) M-1 s-1) than in the absence of heparin. The results suggest that protein C inhibitor may be important in the physiological control of acrosin activity, particularly where the presence of heparin-like glycosaminoglycans would stimulate the acrosin-protein C inhibitor reaction.

Matrix degrading properties of sperm serine proteinase, acrosin

The serine proteinase acrosin plays an important role in sperm penetration of the zona pellucida. In the present study we investigated the effect of the enzyme on various matrix proteins. Acrosin degraded proteolytically fibronectin, type IV collagen and heat denatured type I collagen, whereas neither native type I collagen nor laminin were cleaved by the enzyme. The specific activity of acrosin with type IV collagen as substrate (66.6 g/h/g) was 125-fold higher than that of known type IV collagenase or stromelysin. These results suggest that acrosin may act as a matrix-degrading proteinase.

Antisperm antibody binding to human acrosin: a study of patients with unexplained infertility

OBJECTIVE

Antisperm antibody binding to acrosin was investigated by Western Blotting. The clinical significance of this binding specificity was assessed in a 2-year clinical follow-up.

DESIGN

Consecutive serum samples positive for antisperm antibodies by both enzyme-linked immunosorbent assay and immunobead testing were evaluated for acrosin-binding specificity.

SETTING

The patients were followed in an outpatient setting by private infertility specialists.

PATIENTS

Sixty-five consecutive infertile referral patients with positive antisperm antibody were evaluated. Clinical follow-up was obtained on 8 of 9 females with evidence of antibody binding to acrosin and 19 of 26 females with no specific binding to acrosin.

INTERVENTIONS

Prednisone therapy was given during six courses of intrauterine insemination with husband's sperm. All treatment decisions were made by private physicians independent of the acrosin-binding result.

MAIN OUTCOME MEASURES

Pregnancy status was obtained as part of a 2-year follow-up.

RESULTS

Acrosin-binding specificity was demonstrated in 10 (15%) of the 65 patients. Two of the 8 women (25%) with antibody binding to acrosin and 6 of the 19 women (32%) with antisperm antibodies but no specific binding to acrosin delivered normal children.

CONCLUSIONS

Although antibody-binding specificity to acrosin could be demonstrated, a 2-year clinical follow-up showed no difference in pregnancy rates when compared with women with antisperm antibodies showing no binding specificity to acrosin.

Acrosin biosynthesis in meiotic and postmeiotic spermatogenic cells

It has been widely accepted that mammalian sperm acrosin is first synthesized only in the postmeiotic stages of spermatogenic cells. In this study, we carried out Northern blot analysis of RNAs prepared from purified populations of mouse spermatogenic cells. The acrosin mRNA was obviously found in meiotic pachytene spermatocytes, and the mRNA content markedly increased in postmeiotic round spermatids. Also, the acrosin mRNA in pachytene spermatocytes was functionally associated with polysomes. These results provide evidence that acrosin biosynthesis is already started in meiotic cells and continues through the early stages of spermiogenesis.

Complete localization of the disulfide bridges and glycosylation sites in boar sperm acrosin

Acrosin is a disulfide-bonded two-chain glycoprotein, which belongs to the serine proteinase family and which plays a central role in mammalian fertilization. The amino acid sequence of acrosin from different species has been recently derived by cDNA analysis. Boar sperm acrosin contains twelve cysteine residues forming two interchain and 4 intrachain disulfide bonds. Protein-chemical and mass-spectroscopic analyses of fragments and subfragments obtained by proteolytic and chemical degradation of the isolated protein allowed the unambiguous localization of all disulfide bridges and glycosylation points in boar acrosin. The 12 cysteines and the glycosylated asparagines in the porcine enzyme are absolutely conserved in number and position within all known acrosin sequences. Thus, the disulfide bond and glycosylation patterns outlined here are conserved during evolution and may be important for enzyme function.

Effects of a membrane-bound trypsin-like proteinase and seminal proteinase inhibitors on the bicarbonate-sensitive adenylate cyclase in porcine sperm plasma membranes

Plasma membranes were purified from flagella of porcine cauda epididymal sperm and proteolytic regulation of bicarbonate-sensitive adenylate cyclase was studied. It was found that the epididymal sperm plasma membrane contained a trypsin-like proteinase which inactivated adenylate cyclase. Bicarbonate activates adenylate cyclase as reported previously, but, at the same time, the anions enhance the inactivation of the enzyme by the membrane-bound trypsin-like proteinase. This phenomenon is not due to the direct activation of the proteinase, but closely related to the activation of adenylate cyclase by bicarbonate. It was also found that seminal proteinase inhibitors blocked the inactivation of adenylate cyclase and maintained the bicarbonate activation of the enzyme at high level. Actually, bicarbonate keeps adenylate cyclase fully active in ejaculated sperm, because membrane-bound proteinase is completely inhibited by the seminal proteinase inhibitors. These results suggest that the interactions between membrane-bound proteinase and seminal proteinase inhibitor are involved in the regulation of the bicarbonate-sensitive adenylate cyclase system.

Chicken acrosin: extraction and purification

The objective of the present research was to identify a procedure whereby chicken acrosin could be purified. Acrosin, as evidenced by amidase activity, was extracted with urea most efficiently at a concentration of 6 M. Extraction efficiency was enhanced by spermatozoal lysis prior to admixture with 6 M urea. Lysis was induced by passage of spermatozoal suspensions through a French pressure cell. Acrosin was purified by using gel filtration, chromatofocusing, and affinity chromatography. Based on amidase activity, a 19-fold purification was obtained with a 28% recovery. Native electrophoresis resolved two major protein bands with proteolytic activity. The methods described afford the procurement of milligram amounts of chicken acrosin.

Acrosin activity in spermatozoa from sterile t6/tw32 and fertile control mice

Spermatozoa from sterile t6/tw32 and control fertile +/+, T/tw32, T/t6 mice were compared for their abilities to hydrolyse protein matrices and for their levels of acrosin activity. The data show that the immature and mature gametes from both the experimental and control males hydrolyse protein matrices. The quantitative acrosin assays show, however, that the mature gametes from the intercomplement males have significantly less total acrosin activity than any of the control groups of gametes. These findings suggest that this reduced acrosin activity is an additional phenotypic expression of the intercomplement genotype which results in male sterility.

Molecular cloning of preproacrosin and analysis of its expression pattern in spermatogenesis

Complementary DNA clones for the boar preproacrosin have been isolated from a randomly primed testis cDNA library in lambda gt10 and from an oligo(dT)-primed testis cDNA in lambda gt11. The nucleotide sequence of the 1418-bp cDNA insert includes a 46-bp 5'-untranslated region, an open reading frame of 1248 bp corresponding to 416 amino acids (45.59 kDa) and a 121-bp 3'-untranslated region. The deduced amino acid sequence includes the active-site residues histidine, asparagine and serine of the catalytic triad of the serine proteinase super-family and is colinear with that determined by amino acid sequencing of the boar acrosin light chain and of a small region of the NH2-terminal sequence of the heavy chain. The preproacrosin cDNA contains at the 3' end a 381-bp sequence which codes for an amino acid sequence not yet found in any other serine proteinase. This amino acid sequence is rich in proline (42 out of 127 amino acids) and is suggested to be involved in the recognition and binding of the spermatozoa to the zona pellucida of the ovum. The mRNA for preproacrosin is synthesized as an approximately 1.6-kb-long molecule only in the postmeiotic stages of boar and bull spermatogenesis.

The specificity of two proteinases that cleave adjacent to arginine, C1 esterase and acrosin, for peptide p-nitroanilide substrates

Relative values of Vmax/Km for hydrolysis of 40 peptide p-nitroanilides catalyzed by human Cl-s and human acrosin are reported. For Cl-s, Ac-Lys(gamma Cbz)-Gly-Arg is the optimum sequence, but 25% of the substrates have (Vmax/Km)rel greater than 0.25 compared to this sequence. The best acrosin substrate tested has the sequence Tos-Gly-Pro-Arg, although (Vmax/Km)rel greater than 0.15 for more than half of the substrates. Proline at P2 is preferred by acrosin. Both enzymes prefer arginine at P1 greater than or equal to 3-fold over lysine and will not accept citrulline. In addition, occupancy of site S3 may yield an increase in Vmax/Km of greater than or equal to 10-fold with either enzyme, but many residues are accepted at S2, S3 and S4. Thus, an acrosin assay using Tos-Gly-Pro-Arg p-nitroanilide as a substrate is more than 20-times as sensitive as existing assays with blocked arginine derivatives.

Caprine acrosin. Purification, characterization and proteolysis of the porcine zona pellucida

Acrosin purified from an acidic extract of ejaculated goat spermatozoa migrated as a single 42,000-Mr band in SDS/polyacrylamide-gel electrophoresis. Reduction and alkylation of caprine acrosin produced two polypeptides, one of Mr 40,000 (heavy chain) and the other of Mr 3700 (light chain). The light chain purified by reversed-phase h.p.l.c. was a glycosylated octadecapeptide with an amino acid sequence similar to that of the N-terminal 18 residues of porcine acrosin light chain (78% positional identity). The sequence of the N-terminal 37 amino acids of purified caprine acrosin heavy chain is similar to that of porcine acrosin heavy chain (70% positional identity through 37 residues). Studies with synthetic substrates and synthetic and natural proteinase inhibitors confirmed both the specificity of the purified proteinase for Arg-Xaa and Lys-Xaa bonds and a serine-proteinase mechanism. Purified caprine acrosin hydrolysed the 90 kDa and 65 kDa components, but did not hydrolyse the 55 kDa component of the porcine zona pellucida. The action of the enzyme on the porcine zona pellucida was indistinguishable from that previously reported for porcine acrosin.

Proteinases and their inhibitors in cells and tissues

A large body of evidence has been assembled to indicate the substantial importance of proteolytic processes in various physiological functions. It has recently become clear too that endo-acting peptide bond hydrolases provisionally characterized and classified at present as serine, cysteine, aspartic and metallo together with unknown catalytic mechanism proteinases sometimes act in cascades. They are controlled by natural proteinase inhibitors present in cells and body fluids. In the first part of the present monograph the author was concerned to present an overview on the morphological and physiological approach to localization, surveying reaction principles and methods suitable for visualization of proteolytic enzymes and their natural and synthetic inhibitors. In the second part the roles played by proteinases have been summarized from the point of view of cell biology. The selection of earlier and recent data reviewed on the involvement of proteolysis in the behavior of individual cells reveals that enzymes, whether they be exogeneous or intrinsic, can be effective and sensitive modulators of cellular growth and morphology. There exists a close correlation between malignant growth and degradation of cells. It appears likely that as yet unknown or at least so far inadequately characterized factors that influence the survival or the death of cells may turn out to be proteinases. The causal role of extracellular proteolysis in cancer cell metastases, in stopping cancer cell growth and in cytolysis remains for further investigated. Ovulation, fertilization and implantation are basic biological functions in which proteolytic enzymes play a key role. The emergence of new approaches in reproductive biology and a growing factual basis will inevitably necessitate a reevaluation of present knowledge of proteolytic processes involved. The molecular aspects of intracellular protein catabolism have been discussed in terms of the inhibition of lysosomal and/or non-lysosomal protein breakdown. Peptide and protein hormone biosynthesis and inactivation are still at the centre of interest in cell biology, and a number of proteinases have been implicated in both processes. A number of conjectures partly based on the author's own work have been discussed which suggest the possibility of the involvement of proteolysis in exocytosis and endocytosis. The author's optimistic conclusion is that through the common action of biochemists, cell biologists, cytochemists, and pharmacologists the mystery of cellular proteolysis is beginning to be solved.

Stimulation of high-affinity GTPase by trypsin and trypsin-like proteinases in membranes of human platelets

The influence of various proteinases on GTP hydrolysis was studied in membranes of human platelets. Of the proteinases examined, trypsin, acrosin and a recently described trypsin-like proteinase from bovine sperm, but not chymotrypsin, increased GTP hydrolysis. Similar to what was described previously for hormone-like agents, the stimulation of GTP hydrolysis by the proteinases was only observed at low GTP concentrations, with apparent Km values of 0.2-0.3 microM-GTP. Stimulation of the high-affinity GTPase by the proteinases occurred without apparent lag phase and was constant over a long period of incubation. The proteinase inhibitors leupeptin and soya-bean trypsin inhibitor blocked the stimulation of GTP hydrolysis, but did not reverse the effect of the proteinases. Treatment of platelet membranes with N-ethylmaleimide, which eliminates Gi-protein (inhibitory guanine-nucleotide-binding protein)-related GTPase stimulation by adrenaline, decreased stimulation of GTP hydrolysis by the proteinases only partially. Activation of GTP hydrolysis by the proteinases was partially additive with that caused by adrenaline, whereas thrombin stimulation was not increased further. The data indicate that, similarly to the proteinase thrombin, trypsin and trypsin-like proteinases can activate GTP-hydrolysing protein(s) that exhibit high affinity for GTP in platelet membranes. It is suggested that the proteinases interact in platelet membranes with a receptor site similar to that used by thrombin and that the observed GTPase stimulation is a reflection of a proteinase-receptor interaction with a guanine-nucleotide-binding regulatory protein.

Immunological approach to characterize proacrosin and various acrosin forms in boar and man by monoclonal antibodies

Three different monoclonal rat antibodies, Acr1, Acr2, and Acr3, have been established against boar proacrosin. They are shown by enzyme-linked immunosorbent and immunoblot assays to react with boar proacrosin and several different acrosin molecules derived therefrom during activation. The epitopes detected by the three antibodies are different from each other, one being highly sensitive to reduction and periodate treatment. The antibodies crossreact with various proacrosin and acrosin molecules derived from human sperm extract; they also show indirect immunofluorescent staining of the acrosomal region of ejaculated sperm from normal men but fail to react with round-headed spermatozoa.

Studies of three major proteases associated with guinea pig sperm acrosomes

The major proteases associated with guinea pig sperm were investigated by using immunological and electrophoretic techniques. Three major proteases were detected following sodium dodecyl sulfate-polyacryl-amide gel electrophoresis in gels containing 0.1% gelatin. These enzymes had molecular weights of 47,000, 34,000, and 32,000 relative to reduced protein standards and 58,500, 40,000, and 37,500 relative to unreduced standards. All three protease activities were present in acid extracts of sperm, detergent extracts of sperm, and the soluble acrosomal components of sperm released following induction of the acrosome reaction with the Ca2+-ionophore A23187. As determined by indirect immunofluorescence, an antibody to purified boar acrosin specifically cross-reacted with the acrosomes of guinea pig sperm. Decreased fluorescence was associated with sperm that had lost their acrosomes. Immunoblot analysis demonstrated that this antibody reacted with the 47,000 Mr protease but not the 32,000 and 34,000 Mr proteases. All three proteases were maximally active in the pH 7.0-8.5 region and were inhibited by classical inhibitors of acrosin activity. During a 3-hour incubation period, MgCl2 (10 mM) inhibited the activities of the 32,000 and 34,000 Mr proteases while the 47,000 Mr protease was stimulated. Although these proteases shared properties that would classify them as trypsin-like proteases, only the 47,000 Mr protease could be definitely classified as a member of the proacrosin-acrosin family based upon cross-reaction with an antibody to purified boar acrosin.

Biochemical studies on proacrosin and acrosin from epididymal boar spermatozoa: in vitro translation of boar testicular proacrosin mRNA

An inactive form of acrosin was extracted from epididymal boar spermatozoa utilizing acid pH conditions. When subjected to activation in alkaline environment, this form turns into an enzymatically active species, which exhibits close-related electrophoretic characteristics. Both the precursor and the activated species, when incubated in the presence of thermolysin, give rise to two fastly moving acrosin molecular forms. In order to establish the nature of the true acrosin zymogen, we isolated poly(A+)-RNA from boar testicles, performed its translation in vitro in the presence of [35S]-methionine and reticulocyte lysate, immunoprecipitated the translation products with anti-boar acrosin antibody, and analyzed them by SDS-polyacrylamide gel electrophoresis and autoradiography. A single translation product of molecular weight 55,000 was detected. It is concluded that the polypeptide chain of the boar zymogen is of 55,000; increases in molecular weight are due to post-translational modifications, like glycosylation.

Purification and characterization of an enzyme produced by Treponema denticola capable of hydrolyzing synthetic trypsin substrates

An enzyme from Treponema denticola that hydrolyzes a synthetic trypsin substrate, N-alpha-benzoyl-L-arginine-p-nitroanilide (BAPNA), was purified to near homogeneity, as judged by gel electrophoresis. The molecular weight of the enzyme was estimated to be ca. 69,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and ca. 50,000 by gel filtration on Sephadex G-100. The pH optimum for the hydrolysis of BAPNA was around 8.5. The enzyme was heat labile and irreversibly inactivated at low pH values. Enzyme activity was enhanced by Ca2+, Mg2+, and Ba2+ but inhibited by Mn2+, Hg2+, Co2+, and Zn2+. Metal chelators and sulfhydryl reagents had no effect on this activity. The enzyme was inhibited by certain protease inhibitors such as diisopropyl fluorophosphate, N-alpha-p-tosyl-L-lysine chloromethyl ketone, phenylmethylsulfonyl fluoride, L-1-tosylamide-2-phenylethylchloromethyl ketone, alpha-1-antitrypsin, and soybean trypsin inhibitor. The Km values for BAPNA and N-alpha-benzoyl-L-arginine ethyl ester were 0.05 and 0.12 mM, respectively, and the Vmax values were higher than those observed with trypsin. Although the purified enzyme hydrolyzed some low-molecular-weight synthetic trypsin substrates, it did not hydrolyze casein, hemoglobin, azocasein, azocoll, bovine serum albumin, or gelatin. Thus, this enzyme is probably not a protease but is capable of hydrolyzing ester, amide, and peptide bonds involving the carboxyl group of arginine and lysine.

Inner acrosomal membrane of mammalian spermatozoa: its properties and possible functions in fertilization

The inner acrosomal membrane (IAM) develops during the spermatid stage of differentiation as that portion of the Golgi-derived acrosome granule that tightly associates with the condensing sperm nucleus. In some mammalian species, an electron-dense proteinaceous material accumulates between the IAM and the nuclear envelope, collectively comprising the "perforatorium." Evidence, including its partial purification and its structural resistance to detergents and sonication, suggests that the IAM is an unusually resiliant membrane. Dense paracrystalline arrays of intramembranous particles, a lack of lectin-mediated receptor modulation, and its lack of participation in sperm-egg fusion suggest that the IAM lacks the same degree of fluidity as the egg surface plasmalemma. Observations using monoclonal antibodies, however, suggest that some specific antigenic modulations may be possible within the IAM. Its structural rigidity is of obvious mechanical value during sperm penetration through the zone pellucida. An additional role as a scaffold for putative zona lysin material remains controversial. Biochemical evidence suggests that acrosin, for example, is not entirely soluble and that some remains sperm-associated, depending on the conditions of acrosome disruption. Nevertheless, morphological studies do not agree on acrosin's specific localization to the IAM. Currently there is only very limited information concerning the localization of the other acrosomal enzymes to the IAM. Another possible role for the IAM in some species may be in recognizing the zona pellucida. Evidence for this derives from the observation that fucoidin, a fucose heteropolysaccharide, inhibits guinea pig sperm-zona binding, and bound fucoidin can be localized to the IAM and equatorial regions of the living acrosome-reacted spermatozoa. Finally, the IAM may have a role in early recognition/adhesion with the colemma.

On the interaction of bull and boar acrosins with the zona pellucida of different mammalian species in vitro

Acrosin was prepared from boar and bull spermatozoa and its lytic effect in vitro on the zona pellucida of mouse, golden hamster, rabbit, pig and cow was investigated. Depending upon the species studied, ovarian oocytes, ovulated oocytes and preimplantation embryos were obtained for the experiments. While in golden hamster and rabbit the zona pellucida was removed by both acrosins, this effect was absent for bull acrosin in cow and mouse eggs and for boar acrosin in pig and mouse eggs. In those species in which the zona pellucida was not removed by the acrosins after an incubation period of 2 hours even a prolongation up to 24 hours with higher amounts of acrosin, the addition of acrosomal extracts to the incubation buffer (Tyrode solution pH 7.2) or an increase of the pH value up to 8.6 of the acrosin solution had no effect upon the zona pellucida. Our results indicate that at least in vitro, acrosin does not possess the capacity to lyse the zona pellucida in a species specific fashion. Since the lytic effect of boar and bull acrosin on the zona pellucida of ovarian oocytes and preimplantation embryos is not different from that on ovulated oocytes it can be assumed that neither the maturation of the zona pellucida during oogenesis nor its modification after fertilization, change the susceptibility of the zona pellucida to acrosin digestion.

On the teratogenesis of round-headed spermatozoa: investigations with antibodies against acrosin, an intraacrosomally located acrosin-inhibitor, and the outer acrosomal membrane

Acrosin, the outer acrosomal membrane (OAM) and an acrosin inhibitor were studied in testicular cells and ejaculated spermatozoa of fertile men and in those of an infertile patient with exclusively round-headed spermatozoa in his ejaculates. The investigations were performed with the aid of immunohistochemical techniques using specific antibodies against the three acrosomal markers isolated from boar spermatozoa. The spermatozoa of fertile men exhibit staining for acrosin, the OAM and the acrosin inhibitor in the cap region while the round-headed spermatozoa of the patient are totally negative for the three markers, clearly supporting the conclusions of other authors that round-headed spermatozoa lack acrosomes. The lack of the acrosin system was further substantiated by the gelatin substrate film technique. In the course of normal human spermatogenesis acrosin, the OAM and the acrosin inhibitor we first demonstrable in early round spermatids, namely in identical compartments adjacent to the cell nucleus. During spermatid differentiation the staining for the three markers becomes flattened over the nucleus, resulting in a cap-like structure in testicular spermatozoa. In contrast to the ejaculated round-headed spermatozoa, the early round spermatids in the testis of the infertile patient exhibit fluorescent staining for the three markers in the region adjacent to the nuclear membrane. In the course of further spermiogenesis, the staining did not extend over the nuclear membrane, as was observed during normal spermiogenesis, but became separated from the nuclear membrane, as was observed during normal spermiogenesis, but became separated from the nuclear membrane, was translocated at various locations in the cytoplasm and was finally eliminated with the loss of the cytoplasm. These results are in accordance with the results of electron microscopically investigations on the teratogenesis of round-headed spermatozoa. Furthermore, the developmental pattern of the acrosin inhibitor during normal and abnormal spermiogenesis supports the intraacrosomal location of the acrosin inhibitor recently described by Tschesche et al. (1982).

Evidence of a high molecular weight form of acrosin in boar acrosomal extract

Acrosomal extracts of freshly ejaculated and immediately processed boar spermatozoa were investigated to detect which and how many acrosin molecular forms were present. Electrophoretic analyses of the acrosomal extract showed the presence of only one, slowly migrating, acrosin molecular form. Enzyme-linked-immuno-electro-transfer blot revealed the molecular weight of this form to be about 66 kdalton. Preliminary electrophoretic analyses under nondenaturating conditions of the acrosomal extract previously treated with thermolysin suggested that the approximately 66 kdalton form gives rise to two comigrating acrosin molecular forms.

Boar acrosin is a two-chain molecule. Isolation and primary structure of the light chain; homology with the pro-part of other serine proteinases

Acrosin (EC 3.4.21.10), the major proteinase of mammalian spermatozoa, has been demonstrated to be a two-chain glycoprotein with an Mr-4200 light chain covalently attached to an Mr-37000 heavy chain. Following mercaptolysis of the disulfide bonds, the two chains were separated by high-performance liquid chromatography on a reversed-phase column. Sequence analysis of the isolated light chain (23 amino acid residues) indicated a considerable sequence homology with the bovine chymotrypsinogen activation peptide (6 out of 15 positions with identical amino acids, i.e. 40% identity) and the pro-part of other serine proteinases (17-22% identity), thus suggesting that the acrosin light chain corresponds to the pro-part of the acrosin zymogen. In position 3, the light chain confers a carbohydrate side chain N-glycosidically linked to the acceptor sequence Asn-Xaa-Thr. Evidence is presented that the acrosin light chain is connected via two disulfide bridges to the heavy chain which contains about 320 amino acids including the active-site residues of the proteinase.

Acrosin and the acrosome in human spermatogenesis

Using the indirect immunofluorescent staining technique, the developmental patterns of (pro) acrosin and the outer acrosomal membrane were studied in human spermatogenesis. Specific antibodies against purified acrosin and outer acrosomal membranes from boar spermatozoa were raised in the rabbit and were found to crossreact with (pro)acrosin and outer acrosomal membrane from human spermatogenic cells. It was concluded that (pro)acrosin as well as the molecules building up the outer acrosomal membrane have been highly conserved during mammalian evolution. In the course of human spermatogenesis (pro)acrosin as well as the outer acrosomal membrane first appear in the haploid spermatids; the fluorescent areas of the individual cells steadily increase during spermiogenesis. Staining for acrosin and the outer acrosomal membrane, respectively, was found in identical compartments of the spermatogenic cells in juxtaposition to the nucleus. Round-headed spermatozoa from an infertile patient did not stain for (pro)acrosin or outer acrosomal membrane. The lack of the acrosin system was further substantiated by the gelatin substrate film technique demonstrating the absence of a gelatinolytic protease in round-headed spermatozoa. Hence, round-headed spermatozoa lack the acrosome with its constituent membrane proteins and the acrosin system housed by the acrosome of normal spermatozoa.

Vitamin K-dependent carboxylases from non-hepatic tissues

The presence of vitamin K-dependent carboxylase was investigated in the microsomal fraction of 20 different types of bovine tissue. Except for muscle, veins, lymphocytes and bone membrane, carboxylase was found in all these preparations, albeit in varying amounts. No differences could be detected between these carboxylating systems with respect to their affinity for vitamin K and warfarin. Most of the endogenous substrates had some affinity towards antiprothrombin or antifactor X.