Comparison of the amino acid sequences of human protamines HP2 and HP3 and of intermediate basic nuclear proteins HPS1 and HPS2. Structural evidence that HPS1 and HPS2 are pro-protamines

Proteomic analysis of human sperm reveals changes in protamine 1 phosphorylation in men with infertility

OBJECTIVE

To perform a comprehensive assessment of protamine (P) isoforms and modifications in human sperm with the aim of identifying how P modifications and isoforms are altered in men with reduced sperm motility and low sperm count.

DESIGN

Cross-sectional.

SETTING

Academic medical center.

PATIENTS

A total of 18 men with prior reported pregnancy and normozoospermia (normal sperm), 14 men from couples with infertility and asthenozoospermia (reduced sperm motility), and 24 men from couples with infertility and oligoasthenoteratozoospermia (low sperm count and motility and abnormal sperm morphology).

INTERVENTION(S)

Not applicable.

MAIN OUTCOME MEASURE(S)

Proteomic assessment using both top-down and bottom-up liquid chromatography mass spectrometry (MS) analysis.

RESULTS

A total of 13 posttranslational modifications were identified on P1 and P2 using bottom-up MS, including both phosphorylation and methylation. Top-down MS revealed an unmodified and phosphorylated isoform of P1 and the 3 major isoforms of P2, HP2, HP3, and HP4. Protamine 1 phosphorylation was overall higher in men with male factor infertility compared with those with normal semen analysis (40.5% vs. 32.6). There was no difference in P posttranslational modifications or isoforms of P2 in men with normal vs. abnormal fertility.

CONCLUSION

Human protamines bear a number of posttranslational modifications, with alterations in P1 phosphorylation noted in the setting of male factor infertility.

Direct visualization of pre-protamine 2 detects protamine assembly failures and predicts ICSI success

Histone-to-protamine transition is an essential step in the generation of fully functional spermatozoa in various mammalian species. In human and mouse, one of the two protamine-encoding genes produces a precursor pre-protamine 2 (pre-PRM2) protein, which is then processed and assembled. Here we design an original approach based on the generation of pre-PRM2-specific antibodies to visualize the unprocessed pre-PRM2 by microscopy, flow cytometry and immunoblotting. Using mouse models with characterized failures in histone-to-protamine replacement, we show that pre-Prm2 retention is tightly linked to nucleosome disassembly. Additionally, in elongating/condensing spermatids, we observe that pre-Prm2 and transition protein are co-expressed spatiotemporally, and their physical interaction suggests that these proteins act simultaneously rather than successively during histone replacement. By using our anti-human pre-PRM2 antibody we also measured pre-PRM2 retention rates in the spermatozoa from 49 men of a series of infertile couples undergoing ICSI, which shed new light on the debated relation between pre-PRM2 retention and sperm parameters. Finally, by monitoring 2-pronuclei (2PN) embryo formation following ICSI, we evaluated the fertilization ability of the sperm in these 49 patients. Our results suggest that the extent of pre-PRM2 retention in sperm, rather than pre-PRM2 accumulation per se, is associated with fertilization failure. Hence, anti-pre-PRM2/pre-Prm2 antibodies are valuable tools which could be used in routine monitoring of sperm parameters in fertility clinics, as well as in experimental research programmes to better understand the obscure process of histone-to-protamine transition.

Characterization of Human Sperm Protamine Proteoforms through a Combination of Top-Down and Bottom-Up Mass Spectrometry Approaches

Protamine 1 (P1) and protamine 2 (P2) family are extremely basic, sperm-specific proteins, packing 85-95% of the paternal DNA. P1 is synthesized as a mature form, whereas P2 components (HP2, HP3, and HP4) arise from the proteolysis of the precursor (pre-P2). Due to the particular protamine physical-chemical properties, their identification by standardized bottom-up mass spectrometry (MS) strategies is not straightforward. Therefore, the aim of this study was to identify the sperm protamine proteoforms profile, including their post-translational modifications, in normozoospermic individuals using two complementary strategies, a top-down MS approach and a proteinase-K-digestion-based bottom-up MS approach. By top-down MS, described and novel truncated P1 and pre-P2 proteoforms were identified. Intact P1, pre-P2, and P2 mature proteoforms and their phosphorylation pattern were also detected. Additionally, a +61 Da modification in different proteoforms was observed. By the bottom-up MS approach, phosphorylated residues for pre-P2, as well as the new P2 isoform 2, which is not annotated in the UniProtKB database, were revealed. Implementing these strategies in comparative studies of different infertile phenotypes, together with the evaluation of P1/P2 and pre-P2/P2 MS-derived ratios, would permit determining specific alterations in the protamine proteoforms and elucidate the role of phosphorylation/dephosphorylation dynamics in male fertility.

Identification of a complex population of chromatin-associated proteins in the European sea bass (Dicentrarchus labrax) sperm

A very common conception about the function of the spermatozoon is that its unique role is to transmit the paternal genome to the next generation. Most of the sperm genome is known to be condensed in many species by protamines, which are small and extremely positively charged proteins (50-70% arginine) with the functions of streamlining the sperm cell and protecting its DNA. However, more recently, it has been shown in mammals that 2-10% of its mature sperm chromatin is also associated to a complex population of histones and chromatin-associated proteins differentially distributed in the genome. These proteins are transferred to the oocyte upon fertilization and may be involved in the epigenetic marking of the paternal genome. However, little information is so far available on the additional potential sperm chromatin proteins present in other protamine-containing non-mammalian vertebrates detected through high-throughput mass spectrometry. Thus, we started the present work with the goal of characterizing the mature sperm proteome of the European sea bass, with a particular focus on the sperm chromatin, chosen as a representative of non-mammalian vertebrate protamine-containing species. Proteins were isolated by acidic extraction from purified sperm cells and from purified sperm nuclei, digested with trypsin, and subsequently the peptides were separated using liquid chromatography and identified through tandem mass spectrometry. A total of 296 proteins were identified. Of interest, the presence of 94 histones and other chromatin-associated proteins was detected, in addition to the protamines. These results provide phylogenetically strategic information, indicating that the coexistence of histones, additional chromatin proteins, and protamines in sperm is not exclusive of mammals, but is also present in other protamine-containing vertebrates. Thus, it indicates that the epigenetic marking of the sperm chromatin, first demonstrated in mammals, could be more fundamental and conserved than previously thought. Abbreviations: AU-PAGE: acetic acid-urea polyacrylamide gel electrophoresis; CPC: chromosomal passenger complex; DTT: dithiothreitol; EGA: embryonic genome activation; FDR: false discovery rate; GO: Gene Ontology; IAA: iodoacetamide; LC: liquid chromatography; LC-MS/MS: liquid chromatography coupled to tandem mass spectrometry; MS: mass spectrometry; MS/MS: tandem mass spectrometry; MW: molecular weight; PAGE: polyacrylamide gel electrophoresis; PBS: phosphate buffered saline; SDS: sodium dodecyl sulfate; SDS-PAGE: sodium dodecyl sulfate polyacrylamide gel electrophoresis; TCA: trichloroacetic acid.

Spermatozoal RNAs: what about their functions?

The profound architectural changes that transform spermatids into spermatozoa result in a high degree of DNA packaging within the sperm head. However, the mature sperm chromatin that harbors imprinted genes exhibits a dual nucleoprotamine/nucleohistone structure with DNase-sensitive regions, which could be implicated in the establishment of efficient epigenetic information in the developing embryo. Despite its apparent transcriptionally inert state, the sperm nucleus contains diverse RNA populations, mRNAs, antisense and miRNAs, that have been transcribed throughout spermatogenesis. There is also an endogenous reverse transcriptase that may be activated under certain circumstances. It is now commonly accepted that sperm can deliver some RNAs to the ovocyte at fertilization. This review presents potential links between male-specific genomic imprinting, chromatin organization, and the presence of diverse RNA populations within the sperm nucleus and discusses the functional significance of these RNAs in the spermatozoon itself and in the early embryo following fertilization. Some recent data are provided, supporting the view that analyzing the profile of spermatozoal RNAs could be useful for assessment of male fertility.

Protamine 2 precursors (Pre-P2), protamine 1 to protamine 2 ratio (P1/P2), and assisted reproduction outcome

OBJECTIVE

To determine whether the presence of protamine 2 precursors (pre-P2/P2 ratio) and the protamine 1 to protamine 2 ratio (P1/P2) are related to the assisted reproduction outcome.

DESIGN

Prospective study.

SETTING

Assisted Reproduction Unit and University laboratory.

PATIENT(S)

One hundred two infertile patients undergoing treatment at the Assisted Reproduction Unit of the Hospital Clinic of Barcelona.

INTERVENTION(S)

Intracytoplasmic sperm injection (ICSI) and/or IVF treatment of the infertile patients, sperm protamine analysis through electrophoresis and densitometry, and pre-P2 analysis through Western blot.

MAIN OUTCOME MEASURE(S)

The presence of protamine 2 precursors (pre-P2/P2 ratio), sperm P1/P2 ratio, fertilization rates by IVF and/or ICSI, and pregnancy outcome.

RESULT(S)

Pre-P2/P2 and P1/P2 ratios are positively associated with the pregnancy rate. In addition, the P1/P2 ratio is positively associated with the proportion of embryos obtained by IVF, but not by ICSI. The pre-P2/P2 ratio was not related to the fertilization rate.

CONCLUSION(S)

Decreased pre-P2/P2 and P1/P2 ratios are related to a poor pregnancy outcome, but not with the proportion of embryos obtained after ISCI.

Identification of proteomic differences in asthenozoospermic sperm samples

BACKGROUND

Asthenozoospermia is one of the most common findings present in infertile males, but its aetiology remains unknown in most cases. Present proteomic tools now offer the opportunity to identify proteins which are differentially expressed in asthenozoospermic semen samples and potentially involved in infertility.

METHODS

We compared the expression of 101 sperm protein spots in 20 asthenozoospermic samples to that of 10 semen donor controls using two-dimensional proteomic analysis.

RESULTS

Seventeen protein spots have been identified at different amounts in the asthenozoospermic samples compared with controls. These are cytoskeletal actin-B, annexin-A5, cytochrome C oxidase-6B, histone H2A, prolactin-inducible protein and precursor, calcium binding protein-S100A9 (2 spots), clusterin precursor, dihydrolipoamide dehydrogenase precursor, fumarate hydratase precursor, heat shock protein-HSPA2, inositol-1 monophosphatase, 3-mercapto-pyruvate sulfurtransferase/dienoyl-CoA isomerase precursor, proteasome subunit-PSMB3, semenogelin 1 precursor and testis expressed sequence 12. The detected amount of these proteins enabled the grouping of asthenozoospermic sperm samples in an unsupervised clustering analysis.

CONCLUSIONS

We have identified several proteins present at different amount in asthenozoospermic sperm samples. These proteins could be candidates towards the development of diagnostic markers, and open up the opportunity to gain further insight into the pathogenic mechanisms involved in asthenozoospermia.

Mammalian sperm chromatin structure and assessment of DNA fragmentation

This review article illustrates the biology of mammalian sperm chromatin structure. The possible causes of DNA (deoxyribonucleic acid) fragmentation are discussed. Also available molecular techniques for assessment of mammalian sperm DNA damage are described.

Protamine 2 precursors, protamine 1/protamine 2 ratio, DNA integrity and other sperm parameters in infertile patients

BACKGROUND

The protamine 1-to-protamine 2 ratio (P1/P2) is altered in the sperm cells of some infertile patients. Also, evidence for increased protamine 2 precursors (pre-P2) in a few patients has been reported. But so far, there have been no studies measuring simultaneously these two variables in a large number of patients.

METHODS

We measured the P1/P2 ratio and the presence of pre-P2 using, for the first time, an antibody specific to the precursor pre-P2, together with other sperm parameters in 224 infertile patients. Additionally, the DNA integrity was assessed by terminal transferase dUTP nick-end labelling (TUNEL) in a subset of the samples.

RESULTS

Pre-P2 levels show a significant positive correlation with the P1/P2 ratio, with the presence of other proteins and, at low pre-P2 levels, with TUNEL-positive sperm. An inverse correlation with sperm count, normal morphology and motility was detected.

CONCLUSIONS

The levels of pre-P2 may provide clues into the pathogenic mechanisms of infertility. The increased proportion of pre-P2 in some patients with increased P1/P2 ratio suggests an involvement of pre-P2 processing. The positive correlation between TUNEL-positive sperm and pre-P2 at low pre-P2/P2 ratios also suggests a link between deficient protamine processing and decreased DNA integrity.

Proteomic identification of human sperm proteins

Conventional 1-DE has in the past provided a wealth of information concerning the major sperm proteins. However, so far there are relatively few reports exploiting the potential of the present proteomic tools to identify and to study additional yet-unidentified important proteins present in human spermatozoa. In the present work, 2-DE of proteins extracted from human normozoospermic spermatozoa led to the resolution of over 1000 spots. Subsequent excision from the gels of 145 spots and MALDI-TOF MS analysis allowed the identification of 98 different proteins. The function of these proteins turned out to be energy production (23%), transcription, protein synthesis, transport, folding and turnover (23%), cell cycle, apoptosis and oxidative stress (10%), signal transduction (8%), cytoskeleton, flagella and cell movement (10%), cell recognition (7%), metabolism (6%) and unknown function (11%). As many as 23% of the proteins identified have not been previously described as being expressed in human spermatozoa. The present data provide an important clue towards determining the function of these proteins and opens up the possibility to perform additional experiments.

Protamines and male infertility

Protamines are the major nuclear sperm proteins. The human sperm nucleus contains two types of protamine: protamine 1 (P1) encoded by a single-copy gene and the family of protamine 2 (P2) proteins (P2, P3 and P4), all also encoded by a single gene that is transcribed and translated into a precursor protein. The protamines were discovered more than a century ago, but their function is not yet fully understood. In fact, different hypotheses have been proposed: condensation of the sperm nucleus into a compact hydrodynamic shape, protection of the genetic message delivered by the spermatozoa, involvement in the processes maintaining the integrity and repair of DNA during or after the nucleohistone-nucleoprotamine transition and involvement in the epigenetic imprinting of the spermatozoa. Protamines are also one of the most variable proteins found in nature, with data supporting a positive Darwinian selection. Changes in the expression of P1 and P2 protamines have been found to be associated with infertility in man. Mutations in the protamine genes have also been found in some infertile patients. Transgenic mice defective in the expression of protamines also present several structural defects in the sperm nucleus and have variable degrees of infertility. There is also evidence that altered levels of protamines may result in an increased susceptibility to injury in the spermatozoan DNA causing infertility or poor outcomes in assisted reproduction. The present work reviews the articles published to date on the relationship between protamines and infertility.

Fine resolution of human sperm nucleoproteins by two-dimensional electrophoresis

Human sperm nucleoproteins consist of protamines and histones. Changes in composition of these proteins are thought to correlate with spermatogenesis and may be involved in some instances of male infertility. We sought to separate sperm nucleoproteins including variants of protamine using an improved two-dimensional electrophoretic method, with the aim of comprehensively analysing all sperm nucleoprotein constituents. After extracting nuclear basic proteins from the sperm of normal volunteers, we analysed these proteins on a gel sheet by a radical free, highly reducing method based on Kaltschmidt and Whittmann's two-dimensional electrophoresis. Basic proteins from sperm nuclei were separated clearly into 12 spots. By amino acid sequence analysis, these spots corresponded to protamine 1 (P1)- (five spots), protamine 2 (P2)-related proteins (six spots) and testis-specific histone H2B (one spot). The N-terminal amino acid sequences of the six P2-related proteins were compatible with those of HPI1, HPI2, HPS1, HPS2, HP2 and HP3, and quantitative comparison could be performed. In conclusion, human sperm nucleoproteins including all P2-related variants could be analysed quantitatively with high resolution on a single electrophoretic gel.

Chromatin organization during spermiogenesis inOctopus vulgaris. II: DNA-interacting proteins

In this article we study the proteins responsible for chromatin condensation during spermiogenesis in the cephalopod Octopus vulgaris. The DNA of ripe sperm nuclei in this species is condensed by a set of five different proteins. Four of these proteins are protamines. The main protamine (Po2), a protein of 44 amino acid residues, is extraordinarily simple (composed of only three different amino acid types: arginine (R), serine (S), and glycine (G). It is a basic molecule consisting of 79.5 mol% arginine residues. The rest of the protamines (Po3, Po4, Po5) are smaller molecules (33, 28, and 30 amino acid residues, respectively) that are homologous among themselves and probably with the main Po2 protamine. The ripe sperm nucleus of O. vulgaris also contains a small quantity of a molecule (Po1) that is similar to Po2 protamine. This protein could represent a Po2 protamine-precursor in a very advanced step of its processing. We discuss the characteristics of these proteins, as well as the relation between the complexity of chromatin condensation and the transitions of nuclear proteins during spermiogenesis in O. vulgaris.

Analysis of hamster protamines: primary sequence and species distribution

Basic nuclear proteins were isolated from the sperm of the Syrian hamster Mesocricetus auratus and characterized by gel electrophoresis, amino acid analysis, and sequencing. Analyses of the proteins by gel electrophoresis show that sperm of this species contain both protamines 1 and 2. The two proteins were purified by HPLC and the complete primary sequence of hamster protamine 1 was determined by automated amino acid sequence analysis. The protein sequence was subsequently confirmed by sequencing the PCR-amplified protamine 1 gene. The first forty-two residues of the hamster protamine 2 sequence were obtained by amino acid sequence analysis of the isolated protein, and this sequence was also confirmed and extended by sequencing the gene. Total basic nuclear protein was also isolated from sperm of six other species of hamsters, the protamines were identified by HPLC and amino acid analysis, and the proportion of protamines 1 and 2 in each species was determined. Marked differences in the protamine 2 content of sperm were observed among the different species of hamster. This variation and the high level of sequence similarity between mouse and hamster protamines provide insight into how the two protamines may be organized in sperm chromatin. Mol. Reprod. Dev. 54:273-282, 1999. Published 1999 Wiley-Liss, Inc.

Primary structure of a myohemerythrin-like cadmium-binding protein, isolated from a terrestrial annelid oligochaete

Two isoforms of a cadmium-binding protein (Cd-BP 14a and Cd-BP 14b) were isolated from the terrestrial oligochaete annelid, Allolobophora caliginosa. The complete amino acid sequence of the major isoform Cd-BP 14a (molecular mass: 13441 Da; 119 residues) and the amino-terminal sequence (57 residues) of Cd-BP 14b were determined. The sequence of Cd-BP 14a is highly similar to that of myohemerythrins present in marine invertebrates. Furthermore, as myohemerythrins, Cd-BP 14a and Cd-BP 14b bind two atoms of iron and their ultraviolet/visible spectra are typical of non-heme iron-binding proteins. Three substitutions were found in the amino-terminal half of the proteins at positions 19, 21 and 41. The substitutions at positions 19 and 21 are conservative, whereas that at position 41 consists of the replacement of an aspartate residue in isoform a by a lysine residue in isoform b. To our knowledge, it is the first report of a protein belonging to the hemerythrin family in a terrestrial invertebrate.

Identification of amino acids critical for the DNA binding and dimerization properties of the human retinoic acid receptor alpha. Importance of lysine 360, lysine 365, and valine 361

Retinoic acid receptors (RARs) and retinoid X receptors (RXRs) activate target genes by binding to retinoic acid response elements (RAREs) as heterodimeric, asymmetrical complexes, and display a high degree of cooperativity in binding to RAREs. We have examined here the effect of lysine, cysteine, arginine, histidine, and tyrosine side chain chemical modification on the DNA binding, homo- and heterodimerization properties of the full-length human retinoic acid receptor alpha (hRARalpha). Lysines are the only residues to be engaged in the dimerization with human retinoid X receptor alpha (hRXRalpha) in the absence of DNA, whereas histidines are selectively involved in the homodimerization of hRARalpha in the presence of a RARE. Arginine modification affected the DNA binding activity of each type of dimer, whereas cysteines and tyrosines were primarily involved in the homo- or heterodimerization process in the presence of the same RARE. Modified lysines, interfering with the dimerization with hRXRalpha, were identified by receptor labeling and peptide mapping. They are located in the hormone binding domain eighth heptad repeat, at positions 360 and 365. In keeping with these results, mutation of Lys360, Val361, and Lys365 diminished strongly the DNA binding activity of hRARalpha as a homodimer or a heterodimer. Our results thus provide direct evidence for the differential involvement of basic, polar, or aromatic amino acids in the DNA binding, homodimerization, and heterodimerization properties of hRARalpha. Furthermore, they demonstrate the use of distinct dimerization interfaces and identify the type of amino acids involved in these protein-protein interactions.

Nuclear maturity of human spermatozoa selected by swim-up or by Percoll gradient centrifugation procedures

OBJECTIVE

To investigate the relationship between sperm preparation techniques and nuclear maturity, as evidenced by the electrophoretic profiles of sperm nuclear proteins.

DESIGN

Analysis of sperm nuclear quality in sperm populations used for IVF.

SETTING

Center for infertility and assisted reproductive technology and university departments.

PATIENTS

Twenty-seven men undergoing an infertility work-up.

MAIN OUTCOME MEASURES

Comparative electrophoretic investigation of nucleoproteins extracted from spermatozoa selected by swim-up or Percoll techniques.

RESULTS

Nuclear maturity level is improved after the two methods of selection but is more improved after Percoll. In the two groups, selected spermatozoa contain less histones. Moreover, Percoll gradients appeared to enrich for spermatozoa with less intermediate proteins and more mature nucleoproteins of P2 family than swim-up spermatozoa.

CONCLUSION

Percoll may offer advantages in terms of the quality of the selected spermatozoa that may influence the outcome of assisted conception techniques.

Sequence analysis and structural features of the largest known protamine isolated from the sperm of the archaeogastropod Monodonta turbinata

Protamine of the archaeogastropod mollusc Monodonta turbinata has been isolated and characterized. With a mass of 13,476 Da, it is the largest known protamine. Amino acid sequence of this protamine (106 residues) was established from data provided by automated sequence analysis and mass spectrometry of the protein and of its fragments. The primary structure of the NH2-terminal region exhibits repetitive sequence motifs "Basic-Ser" (mainly R-S) and both central and COOH-terminal regions are composed by arginine clusters. The amino acid sequence of Monodonta turbinata protamine shows structural similarities with other protamines from invertebrates and from birds and mammals.

The nuclear status of human sperm cells

In the last decade, and in particular since the development of in vitro fertilization techniques, the nuclear status of human sperm cells has shown to be a key parameter in the assessment of male fertility. The shape and condensed state of the mature sperm nucleus are determined by structural and functional events that occur during spermiogenesis. This paper reviews essential findings on re-organization of the nucleus during sperm differentiation and maturation, and reports recent data on the architecture, biochemical composition and stability of the nucleus in human ejaculated spermatozoa. Different methods used to evaluate nuclear maturity in relation to male fertility are critically appraised.

Persistence of protamine precursors in mature sperm nuclei of the mouse

During mouse spermiogenesis, two protamines, mP1 and mP2, are synthesized in replacement of histones. One of them (protamine mP2, 63 residues) appears at first in elongating spermatid nuclei as a protamine of 106 residues (pmP2) with an amino-terminal extension that is progressively excised. The two protamines were previously described as the only proteins associated with DNA in sperm chromatin. This paper shows that the nuclear proteins of mouse spermatozoa are indeed heterogeneous: at least six minor polypeptides in addition to protamines can be identified. The primary structure of four of them has been established. They are intermediate in the maturation of the precursor of protamine mP2 and correspond to polypeptides pmP2/11, pmP2/16, pmP2/20, and pmP2/32, characterized previously in mouse testis. Therefore, these intermediates of proteolysis generated from pmP2 inside spermatid nuclei persist in mature sperm, whereas the largest precursors, pmP2 and pmP2/5, disappear. These findings clearly indicate that limited proteolysis events still occur outside of the testis.

Isolation and characterization of a small putative zinc finger protein from cuttlefish epididymal sperm cells

At the end of spermiogenesis, sperm chromatin stabilization is ensured by protamine dephosphorylation and, in mammals, by the formation during epididymal transit, of intra- and inter-molecular disulfide bridges between protamines. In cuttlefish, the nuclear protein transition histones-->spermatid-specific protein T-->protamine Sp is very similar to that occurring in mammals during spermiogenesis. However, in cuttlefish, the protamine Sp is devoid of cysteine residues. The protein complement of cuttlefish epididymal sperm nuclei has been investigated. A minor basic protein, called protein E, has been isolated. Its primary structure was established from sequence analysis and mass spectrometry data of the protein and its fragments. Protein E contains a motif -Cys-Xaa2-Cys-Xaa23-His-Cys-Xaa2-Cys- which is likely to adopt a zinc finger conformation. Reduced protein E does fix zinc whereas alkylation of cysteine residues abolishes this ability. The sequence of protein E does not correspond to that of any known protein, but presents some similarities with a part of ZFY protein, a putative human transcription factor specifically expressed in germinal cells and which could be involved in spermatogenesis.

Production, characterization, and immunocytochemical applications of monoclonal antibodies to human sperm protamines

Three monoclonal antibodies against human protamines were obtained by immunization with total human basic nuclear proteins or purified protamine HP3. The specificity of antibodies was assessed by enzyme-linked immunosorbent assay (ELISA) and Western blot. They recognized three distinct epitopes: One was specific for the protamine P1 family, another was specific for the protamine P2 family and the third was common to both families. All were specific for the human species. Antibodies were used to detect protamines in germ cells by indirect immunofluorescence and by immunoelectron microscopy. Protamines appeared in spermtid nuclei at steps 4-5 of spermiogenesis, i.e., during the chromatin condensation process, and were not accumulated in the cytoplasm before entering the nucleus.

Post-translational chemical modifications of proteins--III. Current developments in analytical procedures of identification and quantitation of post-translational chemically modified amino acid(s) and its derivatives

1. The Chemical modifications of amino acids and their derivatives are mainly due to different post-translational enzymatic reactions. 2. The enzymatic reactions resulting in amino acids such as acetylation-, formylation, methylation-phosphorylation-, sulfation-, hydroxylation, ADP ribosylation-, carboxylation-, amidation-, adenylylation-, glycosylation-, ubiquitination-, prenylation and acylation are listed and analytical methods are reported and extensively reviewed. 3. The post-translationally modified cross-linking molecules after maturations such as desmosines, allo-desmosine, hydroxy-, lysylpyridinoline, 3-hydroxypyridinium derivatives, cyclopentenosine recently found in matured elastin, and in collagen, and pulcherosine a novel tyrosine-derived found in fertilization envelope of Sea Urchin embryo, di-tyrosine in resilin, gamma-glutamyl-lysine isopeptide cross-linking molecule etc. are listed and both physico-chemical and analytical methods are extensively reviewed and discussed. 4. Other consequences of post-translational modifications encountered in the analytical procedure such as N-terminal step-wise Edman degradation of glycosylated site(s), phosphorylated-site(s) and or sulfated-site(s) were also reported by us.

Amino acid sequence of the human intermediate basic protein 2 (HPI2) from sperm nuclei. Structural relationship with protamine P2

Human intermediate basic protein 2 (HPI2) is a low-molecular-mass basic protein present in small amounts in human sperm nuclei. The amino acid composition of the protein, its N-terminal amino acid sequence and peptide maps obtained after digestion with endoproteinases Lys-C and Glu-C, reveal that HPI2 is structurally related to human protamine species P2 (HP2), which is rich in Arg, His and Cys residues. Compared to HP2, which is one of the two major sperm protamines, HPI2 has an N-terminal extension of 24 residues which includes six acidic residues and does not possess any Arg residues. The amino acid sequence of HPI2 (81 residues) is identical to the sequence of the C-terminal region of another minor sperm nuclear protein, human intermediate basic protein 1 (HPI1, 101 residues), which was sequenced previously [Martinage, A., Arkhis, A., Alimi, E., Sautière, P. & Chevaillier, P. (1990) Eur. J. Biochem. 191, 449-451]. Due to this structural similarity, HPI2 must be considered as an intermediate in the maturation of proprotamine HPI1 limited proteolysis.

Molecular cloning and expression of a metallothionein mRNA in Xenopus laevis

Metallothioneins (MT) are expressed during early development in species of several groups. To understand MT function in developmental processes, we studied the MT system of Xenopus laevis, a model vertebrate species in experimental embryology. We first purified and sequenced the liver MT from copper-treated animals. This 62-amino-acid protein shares the main structural properties of known vertebrate MT, and is more closely related to avian than to fish or mammalian MT. Using this sequence, we designed oligonucleotide primers to amplify and isolate a MT clone from a XL2 cell line cDNA library. This 752-bp cDNA encodes a putative 62-amino-acid-long protein that is 100% identical with the sequenced MT. Zinc, cadmium, and copper ions are very efficient inducers of MT mRNA accumulation in Xenopus liver and cell lines.

Human male infertility may be due to a decrease of the protamine P2 content in sperm chromatin

Basic chromosomal proteins were extracted from the sperm of fertile and infertile human males. The relative proportions of protamine 1, 2, and 3 were determined by scanning microdensitometry following electrophoresis of total protamine in polyacrylamide gels. The findings were as follows: (1) The proportion of protamine P(2 + 3) in sperm obtained from infertile males was lower than that in fertile males. (2) Protamine P(2 + 3) in infertile human males showed reduced affinity to DNA. The possibility that some cases of human male infertility may be due to mutation within the protamine P2 gene is discussed.

Immunological evidence for a P2 protamine precursor in mature rat sperm

High molecular weight proteins in Rattus norvegicus that are immunoreactive with an anti-protamine 2 specific antibody but not with an anti-protamine 1 specific antibody are described. These proteins were detected by coupling high-performance liquid chromatography (HPLC) with an enzyme-linked immunosorbent assay (ELISA). Briefly, following HPLC separation of rat sperm nuclear proteins, the HPLC fractions were probed with the antibodies. We estimate that the antibody probes are 100-1000 times more sensitive than UV absorbance measurements. Immunoblot analysis following acid-urea electrophoretic separation of rat sperm nuclear proteins, and of the HPLC fractions, also detected putative protamine 2 precursor proteins. The proteins reactive with the anti-protamine 2 antibody are most likely not mature protamine 2, since they were detected in a region of the chromatogram where we would not expect protamine 2 to migrate based on the chromatographic locations of human and mouse protamine 2. Likewise, the immunoblotting experiments demonstrated that the anti-protamine 2 antibody recognized proteins with slower electrophoretic mobilities than would be expected for a mature protamine 2. An anti-protamine 1 monoclonal antibody, Hup1N, that binds rat protamine 1 is also described. Hup1N allowed for identification of the HPLC fractions that contained rat protamine 1. Finally, we demonstrated that Hup1N binds protamine 1 from a large number of species, suggesting a conserved epitope for Hup1N.

Auto-antibodies to human sperm basic nuclear proteins in infertile and vasectomized men: characterization of antigens and epitopes recognized by antibodies

The sera of vasectomized men and of patients with immune infertility were used to study the antigens and epitopes of sperm nuclear proteins that bind antibodies in these sera. No reaction with sperm histones was observed except for one serum. P1, P2 protamines and pro-P2 protamines were recognized by auto-antibodies. Studies with peptides derived from P1 and P2 protamines and with mammalian protamines related to HP1 showed that antibodies are mainly specific for a folded protamine molecule, more especially antibodies from vasectomized men. These results disagree with the random coil model proposed for protamines by several previous works. A cross-reactivity between P1 and P2 protamines was observed only for the whole molecules and not for peptides derived from them. This observation suggests that the two classes of protamines, different in sequence, may have a similar folding and thereby may be functionally equivalent.

Molecular characterization of six intermediate proteins in the processing of mouse protamine P2 precursor

In mouse spermatozoa, DNA is compacted by two protamines mP1 and mP2. Protamine mP2 (63 residues) is synthesized in spermatid nuclei as a precursor pmP2 (106 residues) which is subsequently processed at the end of spermiogenesis [Yelick, P.C., Balhorn, R., Johnson, P.A., Corzett, M., Mazrimas, J.A., Kleene, K.C. & Hecht, N.B. (1987) Mol. Cell. Biol. 7, 2173-2179]. Six proteins, three of which were described earlier [Chauvière, M., Martinage, A., Debarle, M., Alimi, E., Sautière, P. & Chevaillier, Ph. (1991) C.R. Acad. Sci. 313, 107-112], have molecular and electrophoretic properties similar to those of pmP2. They were isolated from purified testis nuclei and characterized by amino acid composition, N-terminal sequence and peptide mapping. From the amino acid compositions, it appears that all six proteins are rich in arginine, cysteine and histidine and are closely related to pmP2 and mP2. The N-terminal sequence of each protein overlaps a distinct region of the N-terminal part of pmP2. The C-terminal part of protamine mP2 starting at arginine 15 is common to all proteins as assessed by amino acid compositions and peptide maps. All these structural data demonstrate that the six isolated proteins are products of pmP2 precursor processing. The six intermediate proteins pmP2/5, pmP2/11, pmP2/16, pmP2/20, pmP2/26 and pmP2/32 which contain 102, 96, 91, 87, 81 and 75 residues, respectively, are generated from the pmP2 precursor after N-terminal excision of 4, 10, 15, 19, 25 and 31 residues, respectively. The C-terminal sequence of protamine mP2 is strictly identical to that of its precursor; therefore, no maturation occurs in this part of the molecule. At the present time, the proteolytic pathway involved in the amino-terminal processing leading to the mature form of the protamine mP2 (63 residues) has not been elucidated. However, the different representation of six intermediates in the testis suggests that some stages of processing are faster than others or that some cleavage sites are preferred. The proteins described in this paper could result either from stepwise excision of N-terminal residues or from non-sequential cleavages.

P2 protamines from human sperm are zinc -finger proteins with one CYS2/HIS2 motif

P1 (HP1) and P2 (HP2, HP3, HP4) protamines were isolated from human sperm nuclei in the reduced form and their interaction with zinc and cobalt was studied. One zinc atom per molecule of P2 protamines but not of P1 protamine was found. Absorption spectra of P2 protamines with cobalt were characteristic of a tetrahedral complex involving two histidine and two cysteine residues and with one cobalt per molecule. A tetrahedral complex was found neither in P1 protamines nor in P2 protamines alkylated at cysteine or at histidine residues. The zinc finger motif Cys2/His2 of P2 protamines may play a role in stabilization of human sperm chromatin and in inhibition of transcription.

Molecular structure of human protamine P4 (HP4), a minor basic protein of human sperm nuclei

Protamine HP4 is a minor protein which was purified from human sperm nuclei. It was characterized by its amino acid composition, peptide mapping after digestion with highly specific endoproteinases and finally by its amino acid sequence. Protamine HP4 contains high amounts of arginine, cysteine and histidine. The primary structure of the protein was established by sequence analysis of intact protamine and of its fragments. HP4 is a P2-type protamine of 58 residues (Mr 7783) structurally related to human protamines HP2 and HP3 from which it only differs by an amino-terminal extension of one and four residues, respectively. These three protamines exhibit a close structural relationship with mouse protamine mP2. The heterogeneity of protamines in human sperm nuclei is discussed.

Processing of the precursor of protamine P2 in mouse. Identification of intermediates by their insolubility in the presence of sodium dodecyl sulfate

Two basic proteins, protamines P1 and P2, are present in chromatin of mouse spermatozoa. Protamine P1, the less abundant protein in mouse, has a homolog in most mammals, and its synthesis follows a conventional route. In contrast, protamine P2 has been found only in certain other mammals, including humans, and it is synthesized as a precursor nearly twice as long as the mature protein. Processing of this precursor is not yet understood, although it necessarily takes place in elongating spermatids and is likely to play a role in the chromatin condensation occurring in these haploid cells. We have fractionated basic proteins from mouse testis chromatin and have identified six proteins on electrophoretic gels which, like protamines, are insoluble in SDS. All six were also soluble at the same trichloroacetic acid concentration as protamine P2 and were present in chromatin of elongating spermatids. Radioactive labelling patterns acquired by these SDS-insoluble proteins during translation in vitro of testis RNA indicate that the largest represents the precursor of protamine P2, and suggest that the others represent intermediates generated by proteolytic cleavage of the precursor. Results from pulse 3H labelling in vivo were also consistent with the conclusion that a precursor/product relationship exists between these proteins and protamine P2. Conclusions concerning the kinetics of processing have, in addition, been drawn from this data. Hypotheses concerning possible functional roles played by the precursor are presented.

Cuttlefish sperm protamines. 1. Amino acid sequences of two distinct variants

The amino acid sequences of two cuttlefish protamine variants Sp1 and Sp2 have been established from automated sequence analysis and mass spectrometry data. Sp1 (57 residues) and Sp2 (56 residues) have molecular masses of 8410 and 8253 Da, respectively. They are almost identical proteins which differ only by one residue of arginine and the position of two of the serine residues (14 and 37 in Sp1; 13 and 35 in Sp2). With an arginine content of about 77%, cuttlefish protamine is one of the most basic proteins which have ever been characterized and the first typical protamine sequenced in invertebrates. It is closely similar to sperm basic proteins identified in squids but strongly differs from the protamine-like components isolated from the sperm of bivalve molluscs.

Anomalous distribution of nuclear basic proteins in round-headed human spermatozoa

An electrophoretic analysis of nuclear proteins has been carried out in normal and in round-headed human spermatozoa. Results revealed an anomalous distribution of nuclear basic proteins in round-headed spermatozoa. They contained more histones and especially more intermediate proteins and less protamines than normal spermatozoa.

Fractionation of basic nuclear proteins of human sperm by zinc chelate affinity chromatography

Immobilized metal affinity chromatography was investigated for the fractionation of basic nuclear proteins of human sperm. Human sperm nuclei essentially contain two classes of protamines: a protamine of type P1 (HPl), rich in cysteine but with only one histidine, and three protamines of type P2 (HP2, HP3, HP4), rich in cysteine and histidine (nine in protamine HP2), potential ligands for transition metal ions. The critical conditions for metal affinity chromatography were defined: choice of metal, protein material and buffer, type of elution and sample loading. Chromatography of nuclear proteins, without histones and with cysteine residues alkylated by iodoacetamide, was optimum on zinc Chelating Sepharose in a Tris-acetate buffer and elution with an increasing concentration gradient of imidazole. Under these conditions, the two classes of protamines were completely separated. The intermediate basic proteins were further purified by reversed-phase high-performance liquid chromatography. Heterogeneity of binding to zinc of protamine HP1 was demonstrated. The proposed method is simple and reproducible and the recovery of proteins is high. It may be applied to study the expression and function of P1 and P2 protamines, e.g., in the case of infertile men.

Genomic sequences of human protamines whose genes, PRM1 and PRM2, are clustered

Protamines are small, arginine-rich proteins involved in the condensation of sperm chromatin. Using cDNA clones, we have isolated the genes for both human protamines, i.e., protamine 1 (PRM1) and protamine 2 (PRM2), from a human cosmid library. Each of these genes contains a single intron consisting of 91 and 163 bp, respectively. From the 5'-noncoding region of PRM1 664 bp and from the 5'-noncoding region of PRM2 902 bp were determined. Both genes contain typical TATAA and CAAT boxes at conventional distances from the transcription start points, which by using primer extension experiments could be assigned to nucleotides -91 and -110 for PRM1 and PRM2 genes, respectively. Comparison of the 5'-noncoding regions of PRM1 and PRM2 genes reveals 12 different motifs in common, 8 of which are clustered in both genes and could reflect regulatory elements for testis- and spermatid-specific gene expression. Both human genes have been found to be clustered at a distance of 4.8 kb. Comparison of the genomic organization of human and mouse protamine genes revealed greater similarities between the two in the 5'-noncoding region.

Molecular characterization of nuclear basic protein HPI1, a putative precursor of human sperm protamines HP2 and HP3

The largest intermediate basic protein HPI1 (101 residues) from human sperm chromatin was isolated and characterized. The amino acid composition and sequence analysis of the protein and of tryptic peptides together with peptide mapping of endoproteinases Lys-C and Glu-C hydrolysates showed that the C-terminal region (residues 45-101) of HPI1 is identical to protamine HP2. These structural data strongly suggest that protein HPI1 is a precursor of human sperm protamines HP2 and HP3 (57 and 54 residues, respectively) as well as of two other intermediate basic proteins HPS1 and HPS2 (69 and 66 residues, respectively) sequenced previously.

Primary structures of two protamine 2 variants (St2a and St2b) from stallion spermatozoa

Protamines were extracted from stallion sperm cell nuclei, alkylated with iodoacetamide and separated by reversed-phase high-performance liquid chromatography. Two main components, protamine 1 and protamine 2, were obtained. The latter contains two subspecies, separable by acetic acid-urea-polyacrylamide gel electrophoresis. The primary structure of protamine 2a (St2a) was determined by analysis of fragments obtained from purified protamine 2 peak by thermolysin digestion. The digested peptides were separated by acetic acid-urea gel electrophoresis and, after electroblotting onto a polyvinylidene difluoride filter, their amino acid sequences were determined by pulse liquid peptide sequencing. The amino acid sequence of protamine 2b was predicted from the double sequence data of protamine 2 peak by eliminating the amino acid of St2a in each cycle. St2a and St2b were found to contain 62 and 58 amino acid residues, respectively, and they seem to be homologous with type 2 protamines from human and mouse spermatozoa.

Nuclear basic protein transition during sperm differentiation. Primary structure of the spermatid-specific protein S2 from the dog-fish Scylliorhinus caniculus

The remodeling of nucleoproteins during dog-fish spermiogenesis involves two successive nuclear protein transitions: the first from somatic-type histones to transition proteins during the nuclear elongation of spermatids and the second leading to protamine-DNA association in mature spermatozoa. The chromatin of elongating spermatids contains two transition proteins called S1 and S2. The amino acid sequence of protein S1, a polypeptide of 87 residues was determined previously [Chauvière, M., Martinage, A., Briand, G., Sautière, P. & Chevaillier, Ph. (1987) Eur. J. Biochem. 169, 105-111]. In the present paper, we report the elucidation of the primary structure of the minor transition protein S2 established by automated Edman degradation of the protein and of its fragments generated by cleavage at methionine and aspartate residues. S2 contains 80 residues and has a molecular mass of 9726 Da. S2 is mainly characterized by a high content of basic amino acids mostly represented by lysine, a relatively high level of hydrophobic residues, the presence of six phosphorylatable residues and the lack of cysteine. Its amino acid sequence shows that the N-terminal half is highly basic, while the acidic residues are located in the C-terminal part of the protein where more diversity in amino acids is noticed. The two transition proteins S1 and S2 share striking structural similarities. Few but significative similarities have been detected with the mammalian transition protein TP1 [Kistler, W. S., Noyes, C., Hsu, R. & Heinrikson, R. L. (1975) J. Biol. Chem. 250, 1847-1853], suggesting similar functions for all these proteins in chromatin remodeling during sperm differentiation. By contrast, the two dog-fish spermatid-specific proteins are structurally unrelated to sperm protamines and cannot be considered as their precursors.