Cloning and sequencing of cDNAs for rabbit preproacrosin and a novel preproacrosin-related cDNA

Characterisation of an epitope shared by an acrosomal acrosin-like protein and the surface of tammar wallaby (Macropus eugenii) spermatozoa

Monoclonal antibodies (mAb) have been raised against marsupial sperm proteins to provide insights into the molecular nature of marsupial spermatozoa, and the proteins that mediate sperm maturation and interaction with the oocyte. This study reports the production of a mAb, designated WSA-1, which bound acrosomal and surface determinants on tammar wallaby spermatozoa. The acrosomal antigen was first detected in the wallaby testis; however, ejaculated spermatozoa demonstrated whole cell WSA-1 immunoreactivity as a result of binding an epididymal protein. Ultrastructural and agglutination analyses localised the WSA-1 epitope to the acrosomal matrix and the whole sperm plasmalemma. The WSA-1 mAb bound three polypeptides with relative molecular weights of 35, 31 and 15 kDa on western blots under reducing conditions. The N-terminal amino acid sequence obtained for the 35 kDa wallaby sperm polypeptide demonstrated identity with the eutherian acrosomal protein acrosin. The 31 kDa polypeptide was of epididymal origin and will be the subject of a separate study. Further studies of the WSA-1 antigens are likely to provide useful insights into the function and maturation of marsupial sperm since proacrosin has a number of putative roles in eutherian fertilisation, and epididymal proteins are thought to mediate sperm maturation and storage.

Molecular characterization of the 32 kDa boar sperm protease

The purified 32 kDa boar sperm protease, known as the 32 kDa sperminogen, was identified by reverse transcription polymerase chain reaction (RT-PCR) and Northern blot analysis following its partial peptide sequencing. The 32 kDa boar sperm protease was purified from the acid extracts of boar spermatozoa and subjected to CNBr-digestion. The most prominently digested 30 kDa product was purified by HPLC and its peptide sequence was analyzed. NCBI Blast search of the analyzed 21 amino acid sequence revealed that the sequence matched 91% with that of proacrosin. DNA primer was deduced from the analyzed peptide sequence and the 32 kDa protease was further identified by RT-PCR. Upon RT-PCR, 1 Kbp DNA fragment was amplified, which is the expected length if the product was amplified from the proacrosin mRNA, implying that there is no separate mRNA for the 32 kDa sperminogen. To confirm these results, Northern blot analysis was performed. Four DNA probes generated from the exons of proacrosin genomic DNA sequence all detected a single species of mRNA, suggesting that there is no separate mRNA for the 32 kDa sperminogen which might be produced either from the potential separate 32 kDa sperminogen gene or by differential splicing from proacrosin mRNA. These results strongly suggest that the 32 kDa protease is part of the proacrosin/acrosin system, and that the 32 kDa sperminogen might be formed from post-translational processing of proacrosin.

A basic 18-amino acid peptide contains the polysulfate-binding domain responsible for activation of the boar proacrosin/acrosin system

Proacrosin is the zymogen of acrosin, a serine protease localized in the acrosomal matrix of mammalian sperm. Proacrosin/acrosin binds to solubilized zona pellucida glycoproteins (ZPGs) and various polysulfates in a non-enzymatic mechanism. In addition, both polysulfates and ZPGs induce proacrosin activation once they bind to the polysulfate-binding domain (PSBD) of the enzyme. We show here that the peptide (43)IFMYHNNRRYHTCGGILL(60) inhibited the proacrosin activation induced by either fucoidan or ZPGs. In addition, the peptide was recognized by the monoclonal antibody C5F10, which is directed against the PSBD region. Our data suggest that the PSBD is composed of many "subsites" that may or may not interact with each other.

Expression of human proacrosin in Escherichia coli and binding to zona pellucida

Proacrosin is a multifunctional protein present in the sperm acrosome. This study characterizes the expression of human proacrosin in bacteria and assesses zona pellucida binding activity. The cDNA encoding human proacrosin was subcloned in pGEX-3X and pET-22b vectors. In the pGEX system, expression of the full-length fusion protein was not detected. In the pET system, an expression product with an apparent molecular size similar to that expected for the proenzyme (Rec-40, 42-44 kDa) was recognized by a monoclonal antibody to human acrosin, AcrC5F10. A 32-34-kDa protein (Rec-30), not recognized by AcrC5F10 on Western blots, was the major expression product. Proteins of 21 (Rec-20) and 18 (Rec-10) kDa were recovered as insoluble expression products as were Rec-40 and Rec-30, and truncated products from the C terminus were detected in the soluble fraction. Rec-40 and Rec-30 coexisted at any culture time tested. Immune serum raised against Rec-30 (AntiRec-30) stained the acrosomal region of permeabilized human spermatozoa and recognized the recombinant proteins and proacrosin from human sperm extracts. Amino acid sequence analysis indicated that Rec-30, Rec-20, and Rec-10 are N-terminal fragments of proacrosin. The recombinant proteins Rec-40, -30, -20, and -10 were found to interact with homologous (125)I-zona pellucida glycoproteins.

Assignment of chromosomal locus and evidence for alternatively spliced mRNAs of a human sperm membrane protein (hSMP-1)

The gene (HSD-1) coding a human sperm membrane protein (hSMP-1) was isolated from a human testis cDNA expression library using antibodies found in the serum of an infertile woman. HSD-1 was localized to a single locus on chromosome 9 and assigned to band 9p12-p13 by fluorescent in situ hybridization (FISH) mapping and DAPI (4,6-diamidino-2-phenylindole) banding, using rat/human somatic cell hybrids and metaphase chromosomes of human lymphocytes. In rescreening a testis lambdagt10 cDNA expression library, the full-length cDNA (HSD-1) and several truncated cDNAs with heterologous regions were isolated from positive clones. The heterology consisted of deletion, insertion and alteration of the 5'-end. These heterologous truncated fragments may be produced by alternative splicing of mRNAs. Two recombinant prokaryotic expression vectors were constructed with one of the heterologous fragment (clone #26) with and without the alternative 5'-end. Escherichia coli transfected with the construct containing the alternative 5'-end failed to produce the recombinant product, whereas those transfected with the vector lacking the 5'-end produced hSMP-1. DNASIS analysis of the structure of #26 mRNA suggests that the 5'-end has a stable secondary configuration that may maintain the mRNA in an inactivated state, whereby hindering its translation and preventing the expression of the gene.

Site-directed mutagenesis of boar proacrosin reveals residues involved in binding of zona pellucida glycoproteins

Proacrosin, the zymogen form of the serine protease beta-acrosin, is thought to function as a secondary binding molecule between mammalian gametes during fertilization (Jansen et al., 1995: Int J Dev Biol 39, 501-510). The interaction involves strong ionic bonds between positively charged amino acids on proacrosin and negatively charged polysulphate groups on zona pellucida glycoproteins. In this investigation, we identified the basic residues on proacrosin that are important for this binding. Site-directed mutagenesis shows that two groups of amino acids comprising His47, Arg50, and Arg51 together with Arg250, Lys252, and Arg253 are crucial because their deletion or replacement severely reduces affinity for zona glycoproteins. Molecular models of proacrosin reveal that these residues are located along one face of the protein on two exposed surface loops that project over and around the catalytic site. These findings support the hypothesis that polysulphate binding sites on proacrosin are formed by a restricted number of basic amino acids on the surface of the protein, presenting a specific orientation that is complementary to negatively charged sulphate groups on zona glycoproteins. Identification and elucidation of the stereochemistry of these charged moieties will aid design of new kinds of nonsteroidal antifertility agents.

Identification of two cDNA clones encoding small proline-rich proteins expressed in sheep ruminal epithelium

Small proline-rich (SPRR) proteins are markers frequently associated with squamous cell differentiation. They have been proposed to be a novel group of precursor polypeptides for the cornified envelope in epidermal keratinocytes. A plus/minus screening procedure was used to identify cDNA clones expressed in mature but not in neonatal sheep ruminal epithelium. Two clones encoding SPRR proteins were identified and are reported here. Clone 27 encodes an ovine SPRR protein corresponding to the human type-II SPRR protein. Clone 26 encodes an ovine SPRR protein similar to human type-II SPRR protein, but which also contains an N-terminal His-Pro repeat similar to the paired repeats found in the Drosophila paired proteins. The unique combination of a paired domain and an SPRR protein has not been reported prior to this study. The tissue distribution indicates that specific expression of the genes corresponding to these two clones occurs in the epithelium of the ruminant forestomach, and to a lesser extent in skin epithelium. In situ hybridization demonstrated that the SPRR mRNA for both clones were localized in the stratum granulosum, in support of their putative physiological function, i.e. formation of the cornified envelope. Based on Northern blot analysis, mRNA complementary to the two clones appears in the ruminal epithelium by 1 week of age, corresponding to the formation of the stratum granulosum during ruminal epithelial development. The different patterns of changes in amount of mRNA corresponding to these clones during rumen epithelial development indicate that they play different roles in rumen epithelial development.

Synthetic peptides corresponding to alpha-lactalbumin and beta-lactoglobulin sequences with angiotensin-I-converting enzyme inhibitory activity

Novel angiotensin-I-converting enzyme (ACE) inhibitory activities were detected in synthetic peptides corresponding to sequences of beta-lactoglobulin and alpha-lactalbumin and which are known to possess opioid activity. Using hippuryl-histidyl-leucine as substrate, the tetrapeptides beta-lactorphin (Tyr-Leu-Leu-Phe), alpha-lactorphin (Tyr-Gly-Leu-Phe) and beta-lactotensin (His-Ile-Arg-Leu) were shown to have IC50 values of 171.8, 733.3 and 1153.2 microM, respectively. Related dipeptides also inhibited ACE, with Tyr-Leu being the most potent, having an IC50 value of 122.1 microM.