Effect of glycosylation on the heparin-binding capability of boar and stallion seminal plasma proteins

Primary structure determination and physicochemical characterization of DSP-3, a phosphatidylcholine binding glycoprotein of donkey seminal plasma

Major proteins of the seminal plasma in a variety of mammals such as bovine PDC-109, equine HSP-1/2, and donkey DSP-1 contain fibronectin type-II (FnII) domains and are referred to as FnII family proteins. To further our understanding on these proteins, we carried out detailed studies on DSP-3, another FnII protein of donkey seminal plasma. High-resolution mass-spectrometric studies revealed that DSP-3 contains 106 amino acid residues and is heterogeneously glycosylated with multiple acetylations on the glycans. Interestingly, DSP-3 exhibits significantly higher homology to HSP-1 (104 identical residues) than DSP-1 (72 identical residues). Circular dichroism (CD) spectroscopic and differential scanning calorimetric (DSC) studies showed that DSP-3 unfolds at ~45 °C and binding of phosphorylcholine (PrC) - the head group moiety of choline phospholipids - increases the thermal stability. Analysis of DSC data suggested that unlike PDC-109 and DSP-1, which exist as mixtures of polydisperse oligomers, DSP-3 most likely exists as a monomer. Ligand binding studies monitoring changes in protein intrinsic fluorescence indicated that DSP-3 binds lyso-phosphatidylcholine (K_a = 1.08 × 10⁵ M^-1) with ~80-fold higher affinity than PrC (K_a = 1.39 × 10³ M^-1). Binding of DSP-3 to erythrocytes leads to membrane perturbation, suggesting that its binding to sperm plasma membrane could be physiologically significant.

Purification, molecular characterization and ligand binding properties of the major donkey seminal plasma protein DSP-1

Fibronectin type-II (FnII) family proteins are the major proteins in many mammalian species including bull, horse and pig. In the present study, a major FnII protein has been identified and isolated from donkey (Equus hemionus) seminal plasma, which we refer to as Donkey Seminal Plasma protein-1 (DSP-1). The amino acid sequence determined by mass spectrometry and computational modeling studies revealed that DSP-1 is homologous to other mammalian seminal plasma proteins, including bovine PDC-109 (also known as BSP-A1/A2) and equine HSP-1/2. High-resolution LC-MS analysis indicated that the protein is heterogeneously glycosylated and also contains multiple acetylations, occurring in the attached glycans. Structural and thermal stability studies on DSP-1 employing CD spectroscopy and differential scanning calorimetry showed that the protein unfolds at ~43 °C and binding to phosphorylcholine (PrC) - the head group moiety of choline phospholipids - increases its thermal stability. Intrinsic fluorescence titrations revealed that DSP-1 recognizes lyso-phosphatidylcholine with over 100-fold higher affinity than PrC. Further, interaction of DSP-1 with erythrocytes, a model cell membrane, revealed that DSP-1 binding is mediated by a specific interaction with choline phospholipids and results in membrane perturbation, suggesting that binding of this protein to sperm plasma membrane could be physiologically significant.

Protein signatures of seminal plasma from bulls with contrasting frozen-thawed sperm viability

The present study investigated the seminal plasma proteome of Holstein bulls with low (LF; n = 6) and high (HF; n = 8) sperm freezability. The percentage of viable frozen-thawed sperm (%ViableSperm) determined by flow cytometry varied from -2.2 in LF to + 7.8 in HF bulls, as compared to the average %ViableSperm (54.7%) measured in an 860-sire population. Seminal proteins were analyzed by label free mass spectrometry, with the support of statistical and bioinformatics analyses. This approach identified 1,445 proteins, associated with protein folding, cell-cell adhesion, NADH dehydrogenase activity, ATP-binding, proteasome complex, among other processes. There were 338 seminal proteins differentially expressed (p < 0.05) in LF and HF bulls. Based on multivariate analysis, BSP5 and seminal ribonuclease defined the HF phenotype, while spermadhesin-1, gelsolin, tubulins, glyceraldehyde-3-phosphate dehydrogenase, calmodulin, ATP synthase, sperm equatorial segment protein 1, peroxiredoxin-5, secretoglobin family 1D and glucose-6-phosphate isomerase characterized the LF phenotype. Regression models indicated that %ViableSperm of bulls was related to seminal plasma peroxiredoxin-5, spermadhesin-1 and the spermadhesin-1 × BSP5 interaction (R2 = 0.84 and 0.79; p < 0.05). This report is the largest dataset of bovine seminal plasma proteins. Specific proteins of the non-cellular microenvironment of semen are potential markers of sperm cryotolerance.

Seminal plasma AnnexinA2 protein is a relevant biomarker for stallions which require removal of seminal plasma for sperm survival upon refrigeration†

Some stallions yield ejaculates that do not tolerate conservation by refrigeration prior to artificial insemination (AI), showing improvement after removal of most of the seminal plasma (SP) by centrifugation. In this study, the SP-proteome of 10 different stallions was defined through high-performance liquid chromatography with tandem mass spectrometry and bioinformatic analysis in relation to the ability of the ejaculates to maintain semen quality when cooled and stored at 5°C. Stallions were classified into three groups, depending on this ability: those maintaining good quality after direct extension in a commercial extender (good), stallions requiring removal of seminal plasma (RSP) to maintain seminal quality (good-RSP), and stallions, unable to maintain good semen quality even after RSP (poor). Pathway enrichment analysis of the proteins identified in whole equine SP using human orthologs was performed using g: profiler showing enriched Reactome and the Kyoto Encyclopedia of Genes and Genomes pathways related to hexose metabolism, vesicle mediated transport, post translational modification of proteins and immune response. Specific proteins overrepresented in stallions tolerating conservation by refrigeration included a peroxiredoxin-6 like protein, and transcobalamin-2, a primary vitamin B12-binding, and transport protein. Also, the protein involved in protein glycosylation, ST3 beta-galactoside alpha-2,3-sialyltransferase 1 was present in good stallions. These proteins were nearly absent in poor stallions. Particularly, annexinA2 appeared as to be the most powerful discriminant variable for identification of stallions needing RSP prior to refrigeration, with a P = 0.002 and a q value = 0.005. Overall this is the first detailed study of the equine SP-proteome, showing the potential value of specific proteins as discriminant bio-markers for clinical classification of stallions for AI.

Milk proteins interact with goat Binder of SPerm (BSP) proteins and decrease their binding to sperm

Seminal plasma Binder of SPerm (BSP) proteins bind to sperm at ejaculation and promote capacitation. When in excess, however, BSP proteins damage the sperm membrane. It has been suggested that milk components of semen extenders associate with BSP proteins, potentially protecting sperm. Thus, this study was conducted to investigate if milk proteins interact with BSP proteins and reduce BSP binding to goat sperm. Using gel filtration chromatography, milk was incubated with goat seminal plasma proteins and loaded onto columns with and without calcium. Milk was also fractionated into parts containing mostly whey proteins or mostly caseins, incubated with seminal plasma proteins and subjected to gel filtration. Eluted fractions were evaluated by immunoblot using anti-goat BSP antibodies, confirming milk protein-BSP protein interactions. As determined by ELISA, milk proteins coated on polystyrene wells bound to increasing of goat BSP proteins. Far-western dot blots confirmed that BSP proteins bound to caseins and β-lactoglobulin in a concentration-dependent manner. Then, cauda epididymal sperm from five goats was incubated with seminal plasma; seminal plasma followed by milk; and milk followed by seminal plasma. Sperm membrane proteins were extracted and evaluated by immunoblotting. The pattern of BSP binding to sperm membrane proteins was reduced by 59.3 % when epididymal sperm were incubated with seminal plasma and then with skimmed milk (p < 0.05). When epididymal sperm were treated with milk followed by seminal plasma, coating of sperm with BSP proteins was not significantly reduced (57.6 %; p > 0.05). In conclusion, goat BSP proteins have an affinity for caseins and whey proteins. Milk reduces BSP binding to goat sperm, depending whether or not sperm had been previously exposed to seminal plasma. Such events may explain the protective effect of milk during goat sperm preservation.

Functional characterization of the domains of the bovine binder of SPerm 5 (BSP5) protein

BACKGROUND

Bovine BSP5 is a multifunctional protein primarily involved in sperm capacitation. BSP5 consists of long N-terminal part followed by two similar and highly conserved fibronectin type II domains designated A and B.

METHODS

In order to assess the role of these domains in the sperm binding and capacitation processes, we created recombinant individual domains (N, A, B), series of overlapping domains (NA and AB) and full-length BSP5 in an Escherichia coli expression system. The recombinant constructs were also tested for their ability to interact with ligands such as gelatine, heparin, chondroitin sulphate B and phosphatidylcholine liposomes by affinity chromatography and co-sedimentation studies.

RESULTS

With the exception of the N domain, all recombinant constructs retained gelatine, phosphatidylcholine, heparin and chondroitin sulphate B binding activities. Domain-wise studies showed clearly that AB domain is capable of performing its biological functions as well as the full-length protein, as it was able to potentiate heparin-mediated sperm capacitation.

CONCLUSIONS

These results indicate that the C-terminal domain composed of two Fn2 domains is sufficient and crucial to maintain the biological functions of BSP proteins. The N-terminal part of the protein did not bind to any of known BSP5-ligands including epididymal sperm and did not seem to be required for either sperm binding or sperm capacitation. This study also confirmed that glycosylation is not required for BSP-mediated sperm capacitation or any of the binding characteristics displayed by BSP5.

Characterization of recombinant murine binder of sperm protein homolog 1 and its role in capacitation

Sperm capacitation is a maturation step that is deemed to be essential for sperm to fertilize an oocyte. A family of proteins, the binder of sperm (BSP), are known to bind choline phospholipids on sperm membranes and promote capacitation in bulls and boars. Recently, BSP-homologous genes have been identified in the epididymal tissues of human (BSPH1) and mouse (Bsph1, Bsph2). The aim of this study was to determine the binding characteristics of the murine binder of sperm protein homolog 1 (BSPH1) and evaluate its effects on sperm capacitation. Since it is not possible to purify the native BSP proteins from human and mouse in sufficient quantity, a murine recombinant BSPH1 (rec-BSPH1) was produced and used for the functional studies. Similarly to BSP proteins from other species, rec-BSPH1 bound to gelatin, heparin, phosphatidylcholine liposomes, and sperm. Both native BSPH1 and rec-BSPH1 were detected on the head and the midpiece region of sperm, although a stronger signal was detected on the midpiece region when sperm were incubated in a capacitating media containing bovine serum albumin. More importantly, murine rec-BSPH1 was able to capacitate sperm, but was unable to induce the acrosome reaction. These results show that murine epididymal BSPH1 shares many biochemical and functional characteristics with BSP proteins secreted by seminal vesicles of ungulates, and suggest that it might play a similar role in sperm functions.

Proteomic analysis of heparin-binding proteins from human seminal plasma: a step towards identification of molecular markers of male fertility

Glycosaminoglycans, especially heparin, are involved in various cell processes such as apoptosis, cell cycle control, platelet activation, capacitation, acrosome reaction and sperm decondensation. Heparin-binding proteins (HBPs) are essential constituents of human seminal fluid, which bind to sperm lipids containing the phosphorylcholine group and mediate the fertilization process. We utilized a proteomic set-up consisting of affinity chromatography, isoelectric focusing (IEF) coupled with matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry (MALDI TOF/MS) for protein analysis of human HBPs. We resolved 70 different spots on two-dimensional (2-D) gel and subsequently identifi ed these proteins. Forty different types of proteins were identified. Functional analysis revealed that 38% of the proteins belonged to the enzyme category, 20% were involved in RNA processing and transcription, 18% in structure and transport function, and 16% in cell recognition and signal transduction. We also identified 8% of proteins with unknown functions, although their expression in seminal fluid has been documented. Proteins of seminal fluid that bind heparin may be directly involved in sperm capacitation and acrosome reaction (AR), which are the two critical steps for fertilization. This information on HBPs would be useful for identifying potential biomarkers of fertility in the near future.

Identifying useable semen

The "predictors of useable semen" used in most commercial AI centers provide a very conservative estimate of the relative fertility of individual boars. Furthermore, the relatively high sperm numbers used in commercial AI practice (usually >3 x10(9) total sperm per dose of extended semen) usually compensate for reduced fertility, as can be demonstrated in some boars when lower numbers of sperm are used for AI. Differences in relative boar fertility are also masked by the widespread use of pooled semen for commercial AI in many countries. However, the need to continually improve the efficiency of pork production, suggests that commercial AI practice should involve increased use of boars with the highest genetic merit for important production traits. Necessarily, this must be linked to the use of fewer sperm per AI dose, fewer inseminations per sow bred, and hence more sows bred by these superior sires. In turn, this requires improved techniques for evaluating semen characteristics directly related to the fertilization process, such as IVM-IVF assays, analysis of seminal plasma protein markers, more discriminatory tests of sperm motility and morphology, with the goal of identifying high-index boars whose fertility is sustained when low numbers of sperm are used for AI. This paper reviews the current status of laboratory-based boar semen evaluation techniques that meet these criteria.

The Lipid Composition Modulates the Influence of the Bovine Seminal Plasma Protein PDC-109 on Membrane Stability

The bovine seminal plasma protein PDC-109 exerts an essential influence on the sperm cell plasma membrane during capacitation. However, by any mechanism, it has to be ensured that this function of the protein on sperm cells is not initiated too early, that is, upon ejaculation when PDC-109 and sperm cells come into first contact, but rather at later stages of sperm genesis in the female genital tract. To answer the question of whether changes of the bovine sperm lipid composition can modulate the effect of PDC-109 on sperm membranes, we have investigated the influence of PDC-109 on the integrity of (i) differently composed lipid vesicles and of (ii) membranes from human red blood cells and bovine spermatozoa. PDC-109 most effectively disturbed lipid membranes composed of choline-containing phospholipids and in the absence of cholesterol. The impact of the protein on lipid vesicles was attenuated in the presence of cholesterol or of noncholine-containing phospholipids, such as phosphatidylethanolamine or phosphatidylserine. An extraction of cholesterol from lipid or biological membranes using methyl-beta-cyclodextrin caused an increased membrane perturbation by PDC-109. Our results argue for a oppositional effect of PDC-109 during sperm cell genesis. We hypothesize that the lipid composition of ejaculated bull sperm cells allows a binding of PDC-109 without leading to an impairment of the plasma membrane. At later stages of sperm cell genesis upon release of cholesterol from sperm membranes, PDC-109 triggers a destabilization of the cells.

Sperm-binding fibronectin type II-module proteins are genetically linked and functionally related

Fibronectin type II (Fn2) module-containing proteins in the male genital tract are characterized by different numbers of Fn2 modules. Predominantly two classes exist which are distinct by having either two or four Fn2 modules. Minor variants with three Fn2 modules were also found in the human and the porcine epididymis. To reveal their relationship, mRNAs and proteins of representatives of these classes were studied in human, in Sus scrofa, and in rodents. Adult boars expressed members of both classes, i.e. ELSPBP1 and pB1, in subsequent regions of the epididymis, and both were under androgenic control. Human and rodent epididymides, on the other hand, alternatively contained only representatives of one of these two classes, i.e. ELSPBP1 in the human and two different pB1-related counterparts in rodents. ELSPBP1 and pB1-related genomic sequences were closely linked in chromosomal regions HSA 19q and SSC 6 q11-q21; conserved synteny between these regions is well established. On the other hand, in a syntenic region on mouse chromosome 7, ELSPBP1-related sequences were lacking. Tight binding to the sperm membrane via a choline-mediated mechanism was a common feature of the two classes of Fn2-module proteins, suggesting related function(s). However, differences in their regionalized expression patterns along the male genital tract as well as in association sites on the sperm surface suggested a species-specific sequential order in sperm binding.

The role of stallion seminal proteins in fertilisation

Seminal plasma proteins are secretory proteins originating mainly from the epididymis and the accessory sex glands. They are involved in the remodelling of the sperm surface which occurs during sperm transit through the male genital tract and continues later at ejaculation. During this process, collectively called post-testicular sperm maturation, the spermatozoa acquire the ability to fertilise an egg. Seminal plasma proteins have been shown to contribute to early and central steps of the fertilisation sequence, e.g. the establishment of the oviductal sperm reservoir, modulation of capacitation and gamete interaction. The major equine seminal plasma proteins belong to three protein classes, which contain widely occurring protein modules. Fn-2 type proteins are characterised by two or four tandemly arranged Fn-2 modules and have been implicated in the modulation of sperm capacitation. Multiple members of the cysteine-rich secretory proteins (CRISP) have been identified in the male genital tract of a number of species. CRISP proteins have been shown to be involved in various functions related to sperm-oocyte fusion, innate host defense function and ion channel blockage. Spermadhesins occur only in ungulate species. Their carbohydrate- and zona pellucida-binding properties would suggest a role of these proteins in gamete recognition. The major proteins of equine seminal plasma have been isolated and characterised regarding their expression along the male genital tract, protein structure and their functions.

Boar spermatozoa in the oviduct

In the pig, a functional tubal sperm reservoir (SR) is established before ovulation to ensure availability of suitable numbers of viable spermatozoa for fertilization. The boar's large ejaculate is split: most spermatozoa are delivered in a sperm-rich fraction (SRF) followed by a post-SRF fraction containing increasing amounts of the spermadhesin PSP-I/PSP-II-rich seminal vesicle secretion. This heterodimer acts as leukocyte chemoattractant both in vitro and in vivo, contributing to the phagocytosis of those spermatozoa not reaching the SR. Sequential ejaculate deposition of marked spermatozoa and SR screening showed that most spermatozoa in the SR arose from the fortuitous PSP-poor, first portion of the SRF fraction, escaping phagocytosis and replenishing the SR within 2-3 h. The SR-sperm numbers diminish gradually in relation to ovulation, spermatozoa being continuously redistributed toward the upper isthmus. In vitro, only uncapacitated spermatozoa bind to epithelial explants, suggesting that the SR influences sperm capacitation. In vivo, most viable spermatozoa--usually harbored in the deep furrows in the pre- or peri-ovulatory SR during spontaneous standing estrus--are uncapacitated, but capacitation significantly increases after ovulation. Pre-/peri-ovulatory SR spermatozoa promptly capacitate in vitro when exposed to the effector bicarbonate, an influence that can be reversed by co-incubation with SR fluid or its component hyaluronan. Fluid collected from the ampullar segment (rich in bicarbonate) induces capacitation in vitro. In conclusion, the lack of massive sperm capacitation in the SR and the diverse individual response to capacitation shown by tubal spermatozoa would relate both to the insurance of full sperm viability before ovulation and the presence of spermatozoa at different stages of capacitation in the upper oviduct, thus maximizing the chances of normal fertilization.

Structural and molecular characterization of equine sperm-binding fibronectin-II module proteins

Phospholipid-binding proteins in the male genital tract are characterized by differing numbers Fn-2 modules (B-domain) carrying N-terminal extensions (A-domain) of variable length. In the stallion, three different proteins were identified, SP-1, SP-2, and EQ-12. SP-1 and SP-2 of the AA'BB'- and ABB'-type, respectively, are major proteins of the seminal plasma. Here we report the cDNA sequences of SP-1, and of a new member of the SP-2 family (SPnew) and the partial characterization of their iso- and glycoforms. The phosphorylcholine (PC)-binding ability of the long Fn-2 protein, EQ-12, with four tandemly arranged Fn-2 modules was determined by PC-affinity chromatography. Expression patterns of EQ-12, and the SP-proteins were studied by means of RT-PCR, Northern blot analysis and immunological approaches indicating differential expression along the male reproductive tract. The vast majority of the short SP-1 and SP-2 proteins are produced by the ampulla whereas EQ-12 originates from the epididymis. Indirect immunofluorescence microscopy of sperm isolated from different regions of the epididymis and Western blot analysis indicate that both, the long and the short Fn-2 proteins associate to the sperm surface during post-testicular maturation. Sperm binding of Fn-2 proteins at the post-acrosome and midpiece was at first detected in the corpus epididymis. Enhanced fluorescence intensity after ejaculation point to an increased number of molecules bound to the sperm surface. The function of these proteins is discussed in regard to their structure-function relationships.

Boar Seminal Plasma Proteins and Their Binding Properties. A Review

Binding properties of a group of proteins isolated from boar seminal plasma and their role in the fertilization process are discussed. Boar seminal plasma contains different types of proteins: spermadhesins of AQN and AWN family, 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 are formed. Sperms coated with proteins participate in different types of interactions in the following steps of the fertilization process: formation of oviductal sperm reservoir, sperm capacitation, oocyte recognition and sperm binding. Saccharide-based interactions of boar seminal plasma proteins play role in the binding of sperm to oviductal epithelium, in sperm capacitation and primary binding of sperm to zona pellucida. An interaction with phospholipid components is responsible for the protein adsorption to sperm membrane. Interactions between proteins participate in the arrangement and remodelling of sperm-coating layers. Study of boar seminal plasma proteins, their characterization and elucidation of their interactions will contribute to understanding the fertilization process. A review with 82 references.

Influence of porcine spermadhesins on the susceptibility of boar spermatozoa to high dilution

The effect of heparin-binding and non-heparin-binding spermadhesins on the viability, motility, and mitochondrial activity of boar spermatozoa at the high dilution (300,000 sperm/ml) to which sperm are exposed during the process of sex sorting by flow cytometry was investigated. Incubation of spermatozoa with heparin-binding spermadhesins caused a time- and dose-dependent decrease in the percentage of functional spermatozoa. The percentage of viable spermatozoa incubated at 38 degrees C with heparin-binding spermadhesins diluted in PBS (1 mg/ml) dropped from 75% (0.5 h) to 4% (5 h), whereas the percentage of viable spermatozoa incubated in PBS without proteins (control) decreased from 85% (0.5 h) to 19% (5 h). Addition of non-heparin-binding PSP-I/PSP-II spermadhesin to the PBS resulted in a concentration-dependent increment of the percentage of viable cells (65% after 5-h incubation), with maximum effect at 1.5 mg/ml. The heparin-binding spermadhesins totally suppressed sperm motility and mitochondrial activity after 5 h of incubation. The same parameters of sperm incubated in the presence of 1.5 mg/ml of PSP-I/PSP-II were 50% and 58%, respectively, and the percentages of control sperm displaying motility and mitochondrial activity were 21% and 26%, respectively. Moreover, the viability, motility, and mitochondrial activity all decreased on incubation of spermatozoa with mixtures of PSP-I/PSP-II and heparin-binding spermadhesins as the concentration of the latter increased. We conclude that PSP-I/PSP-II and the heparin-binding spermadhesins exert antagonistic effects on the functionality of highly diluted boar spermatozoa. The finding that PSP-I/PSP-II contributes to maintaining sperm with high viability, motility, and mitochondrial activity for at least 5 h at physiological temperature points to its potential use as an additive for sperm preservation, specifically of highly diluted, flow-sorted spermatozoa for sex preselection.

Two-dimensional polyacrylamide gel electrophoresis map of bull seminal plasma proteins

A two-dimensional polyacrylamide gel electrophoresis map of bull seminal plasma proteins has been established. About 250 spots were detected after silver staining and polypeptides from 24 spots have been N-terminally sequenced. Major proteins already described in bull seminal plasma, like PDC-109 and aSFP, have been located on the map; proteins not yet reported in male reproductive tracts have been evidenced; for some polypeptides showing a previously unknown N-terminal sequence, structural similarities with proteins described in other organisms have been found. A reference map of seminal plasma proteins could be useful in relating protein pattern changes to physiopathological events influencing the reproductive sphere.

Biochemical and conformational characterisation of HSP-3, a stallion seminal plasma protein of the cysteine-rich secretory protein (CRISP) family

HSP-3 is a member of the cysteine-rich secretory protein (CRISP) family from stallion seminal plasma. We report a large-scale purification protocol for native HSP-3. This protein is a non-glycosylated polypeptide chain with a pI of 8-9 and an isotope-averaged molecular mass of 24987 +/- 3 Da. The molecular mass of HSP-3, determined by equilibrium sedimentation, is 26 kDa, showing that the protein exists in solution as a monomer. The concentration of HSP-3 in the seminal plasma of different stallions ranged from 0.3 to 1.3 mg/ml. On average, 0.9-9 million HSP-3 molecules/cell coat the postacrosomal and mid-piece regions of an ejaculated, washed stallion spermatozoon, suggesting a role in sperm physiology. Conformational characterisation of purified HSP-3 was assessed by combination of circular dichroism and Fourier-transform infrared spectroscopies and differential scanning microcalorimetry. Based on secondary structure assignment, HSP-3 may belong to the alpha+beta class of proteins. Thermal denaturation of HSP-3 is irreversible and follows a non-two state transition characterised by a Tm of 64 degrees C, an enthalpy change of 75 kcal/mol, and a van 't Hoff enthalpy of 184 kcal/mol. Analysis of the spectroscopic and calorimetric data indicates the occurrence of aggregation of denatured HSP-3 molecules and suggests the monomer as the cooperative unfolding unit.

Isolation and characterization of heparin- and phosphorylcholine-binding proteins of boar and stallion seminal plasma. Primary structure of porcine pB1

In the bovine, seminal plasma heparin-binding proteins bind to sperm lipids containing the phosphorylcholine group and mediate the capacitating effects of heparin-like glycosaminoglycans during sperm residence in the female genital tract. We report the characterization of heparin- and phosphorylcholine-binding proteins of stallion and boar seminal plasma. Horse seminal plasma proteins HSP-1 and HSP-2, and boar protein pB1, belong to the same family as the bull heparin- and phosphorylcholine-binding proteins BSP-A1/2, BSP-A3, and BSP-30K. We have determined the amino acid sequence and posttranslational modifications of boar glycoprotein pB1. It contains 105 amino acids arranged into a mosaic structure consisting of a N-terminal 18-residue O-glycosylated polypeptide followed by two tandemly organized 40-45-residue fibronectin type II domains. pB1 displays 60-65% amino acid sequence similarity with its equine and bovine homologues. However, in their respective seminal plasmas, the BSP and the HSP proteins associate into 90-150-kDa oligomeric complexes, whereas pB1 forms a 35-40-kDa complex with spermadhesin AQN-1. In addition, pB1 appears to be identical to the recently described leukocyte adhesion regulator of porcine seminal fluid pAIF-1. Our results tie in with the hypothesis that homologous proteins from different mammalian species may display distinct biological activities, which may be related to species-specific aspects of sperm physiology.

The primary structure of BSP-30K, a major lipid-, gelatin-, and heparin-binding glycoprotein of bovine seminal plasma

BSP-30K is a major acidic glycoprotein of bovine seminal plasma. It displays heparin-, gelatin-, and phospholipid-binding activities. BSP-30K binds to spermatozoa upon ejaculation and is thought to play a role in sperm capacitation. We have determined its amino acid sequence, disulfide bonds, and 0-glycosylation sites. BSP-30K consists of 158 amino acids arranged in a mosaic structure. BSP-30K has a unique 48-residue N-terminal extension which includes three 7-8- amino acid repeats and the six O-glycosylated threonine residues. The polypeptide stretch 49-71 is homologous to type 'A' domains found in heparin-binding proteins from other mammalian species. The C-terminal portion of BSP-30K is organized in a tandem of 40-44-residue domains each sharing the consensus pattern of the gelatin-binding fibronectin type II module. The mosaic structure of BSP-30K suggests that this glycoprotein might be a factor contributing to the different sperm-capacitating effects exerted by heparin in different mammalian species.