Protamines. II. Circular dichroism study of the three main components of clupeine

A sperm nuclear basic protein from the sperm of the marine worm Chaetopterus variopedatus with sequence similarity to the arginine-rich C-termini of chordate protamine-likes

The sperm nuclear basic proteins (SNBPs) of the marine annelid worm Chaetopterus variopedatus have been shown previously to consist of a mixture of two SNBPs: histone H1-like (CvH1) and C.variopedatus protamine-like (CvPL). Here, we report the structural characterization of CvPL. The protein has a molecular weight of 8370.5 Da, a K/R ratio of 0.34, and a secondary structure, which are intermediate between those of protamine (P) and protamine-like (PL) SNBPs. The N-terminal sequence of CvPL shows a high extent of similarity with the arginine-rich C-terminal domain of chordate PL-type SNBPs. Furthermore, the protein binds to DNA in a similar fashion as vertebrate PLs and their own CvH1, but in a way that is different from that of the lysine-rich somatic H1 histones. We have experimentally determined the molar ratio CvH1:CvPL to be ∼1:6 in C. variopedatus sperm. Based on all of these, a model is proposed for the organization of the sperm chromatin by CvH1 and CvPL.

Osteoconductive protamine-based polyelectrolyte multilayer functionalized surfaces

The integration of orthopedic implants with host bone presents a major challenge in joint arthroplasty, spinal fusion and tumor reconstruction. The cellular microenvironment can be programmed via implant surface functionalization allowing direct modulation of osteoblast adhesion, proliferation, and differentiation at the implant--bone interface. The development of layer-by-layer assembled polyelectrolyte multilayer (PEM) architectures has greatly expanded our ability to fabricate intricate nanometer to micron scale thin film coatings that conform to complex implant geometries. The in vivo therapeutic efficacy of thin PEM implant coatings for numerous biomedical applications has previously been reported. We have fabricated protamine-based PEM thin films that support the long-term proliferation and differentiation of pre-osteoblast cells on non-cross-linked film-coated surfaces. These hydrophilic PEM functionalized surfaces with nanometer-scale roughness facilitated increased deposition of calcified matrix by osteoblasts in vitro, and thus offer the potential to enhance implant integration with host bone. The coatings can make an immediate impact in the osteogenic culture of stem cells and assessment of the osteogenic potential of new therapeutic factors.

Secondary structure of protamine in sperm nuclei: an infrared spectroscopy study

Background

Protamines are small basic proteins that condense the DNA in mature spermatozoa. Typical protamines are of simple composition and very arginine-rich, usually in the range of 60-80%. Arginine residues are distributed in a number of stretches separated by neutral amino acids. We have used Fourier transform infrared spectroscopy (FTIR) to gain access for the first time to the secondary structure of protamines in sperm nuclei. This technique is particularly well suited to the study of DNA-bound protamine in whole nuclei since it is not affected by turbidity.

Results

We show that DNA -bound salmon (salmine) and squid protamines contain α-helix, β-turns and a proportion of other structures not stabilized by intramolecular hydrogen bonding. No β-sheet was observed. In salmine, the α-helix amounted to ~20%, while in squid protamine it reached ~40%. In contrast, the structure not stabilized by intermolecular hydrogen bonding was more abundant in salmine (~40%) than in squid protamine (~20%). Both protamines contained ~40% β-turns. The different helical potential of salmine and squid protamine was confirmed by structure predictions and CD in the presence of trifluoroethanol.

Conclusion

DNA-bound protamine in sperm nuclei contains large amounts of defined secondary structure stabilized by intramolecular hydrogen bonding. Both salmine and squid protamine contain similar amounts of β-turns, but differ in the proportions of α-helix and non-hydrogen bonded conformations. In spite of the large differences in the proportions of secondary structure motifs between salmon and squid protamines, they appear to be equally efficient in promoting tight hexagonal packing of the DNA molecules in sperm nuclei.

Helical structure of basic proteins from spermatozoa. Comparison with model peptides

We describe structural studies carried out with some basic proteins found in association with DNA in the spermatozoa of molluscs and echinoderms. We have studied proteins related to histone H1 as well as protamines. Structural prediction methods show that these proteins have a strong helical potential and contain several turns, mainly of the SPKK type. No beta structures were found. Strong structural similarities have been detected between distantly related species. The presence of helical regions is confirmed by circular dichroism in trifluoroethanol solution. The influence of the SPKK turns is also evident in the CD spectra. In proteins which contain a high percentage of arginine we conclude that conventional prediction methods should be modified in order to allow for a higher helical potential for this amino acid residue. Synthetic peptides with a sequence present in the C-terminal region of histone H1 have also been studied. It was found that octapeptides may only acquire a small amount of structure, whereas hexadecapeptides are 50-60% helical. These studies strongly suggest that both protamines and proteins related to the C-terminal part of histone H1 interact with DNA mainly in the alpha-helical conformation.

Studies on the function mechanism of a Formosan grey mullet protamine-mugiline beta M6: interaction of the M6 and M6 fragments with DNA

The interaction of three peptide segments of one component of Formosan grey mullet protamine (mugiline beta M6), obtained by chemical and enzymatic cleavage, with DNA was studied by spectroscopic measurement, thermal denaturation and circular dichroism. The data obtained were then compared with those of whole M6 and other fish protamines such as salmine of salmon and clupeine of herring. M6-B-I, which lacks C-terminal 11 amino acids in M6, showed significantly different properties. It showed remarkably high DNA aggregating ability which was due to a conformational change of DNA from B to A form. The conformational change of DNA induced by the binding of M6-B-I was reproduced by the carboxypeptidase B digestion of DNA-M6 complex. From these results, the arginine-rich, C-terminal domain of the M6 molecule was estimated to be essential for natural DNA binding.

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.

Hydration of clupeine in solution

Spin-lattice relaxation times, T1, of H2(17) O at 25 degrees were measured for aqueous solutions of clupeine and its constituent amino acids, which are serine, threonine, proline and arginine. The dynamic hydration numbers, nDHN, of clupeine and amino acids were determined from a concentration dependence of T1. The coordination numbers nh, and the rotational correlation times, tau ch, of water molecules around clupeine and amino acids were estimated and compared with that of pure water. The tau ch/tau co of clupeine was 1.85 and close to that of arginine. The experimental value of nDHN of clupeine was in good agreement with that calculated from the nDHN values of the constituent amino acids. This means that the clupeine molecule has a random conformation in solution.

Sequence and characterization of the sperm-specific protein phi 3 from Mytilus californianus

We have shown that the sperm-specific protein phi 3 from Mytilus californianus (Conrad) exhibits compositional microheterogeneity. For the first time, we have isolated and characterized the three major components of this protein. These fractions display different electrophoretic mobilities on Triton/urea/acetic acid polycrylamide gels. However, they have a very similar molecular mass of 5 +/- 0.1 kDa as measured by sedimentation equilibrium in the analytical ultracentrifuge. All of them show a marked trend toward aggregation. We have also established the sequence for each of these three fractions. The sequencing data suggest an even greater extent of microheterogeneity for this protein. The predicted secondary structure from the sequences, as well as infrared analyzes carried out on the native protein, suggest a structure organization into an alpha helix.

Nuclear magnetic resonance of protamines. A 1H-NMR study of the interaction of clupeine fractions with mononucleotides

The interaction of the three clupeine fractions, YI, YII, Z, and salmine fraction AI with mononucleotides has been examined by means of 1H nuclear magnetic resonance. The results obtained are interpreted in terms of electrostatic interactions between positive arginine guanidinyl groups and negative nucleotide phosphates. In addition, clupeine fraction YI and salmine fraction AI exhibit with guanine and adenine nucleotides a more specific interaction that leads to the formation of large aggregates in solution. The experimental data presented in this work demonstrate that the strength of interaction between clupeine YI and salmine AI with mononucleotides follows the order: 5'-dTMP approximately equal to 5'-dCMP much less than 5'-dAMP less than 5'-dGMP approximately equal to 5'-GMP.

The effect of counterions on melittin aggregation

Melittin, a surface-active polypeptide from bee venom, has an overall hydrophobic N-terminus, with basic residues clustered at the C-terminus. In aqueous solution melittin exists as a mixture of monomer and tetramer, the monomer adopting a predominantly random-coil configuration, whereas the tetramer is rich in alpha-helix. The tendency of melittin to aggregate is dependent on the counter-anions present in solution, the effect being most marked with phosphate, decreasing in the order HPO4(2-) greater than SO4(2-) greater than ClO4- greater than Cl-.

Interaction of the three main components of clupeine with glycosaminoglycans

The interactions between each of the three main components of clupeine (YI, YII and Z) and the glycosaminoglycans chondroitin sulfate, heparin and hyaluronic acid were studied with circular dichroism spectroscopy. The induced dichroism is a measure of relative complex stability, which increases with the number of sulfate groups on the glycosaminoglycan. Measuring the induced dichroism as a function of mole ratio of disaccharide to arginine establishes the stoichiometry of the complexes. For a given glycosaminoglycan, the induced dichroism depends on the clupeine, increasing the order YI less than YII less than Z.

Preparation and conformational study of clupeine fragments

Fragments of clupeines, YI, YII, and Z of divergent chain length and different amino acid composition were prepared by digestion with thermolysin and a mixture of carboxypeptidases A and B, and their conformational preferences examined as a function of pH, added salts, presence of a helix-supporting solvent, and temperature. All these highly basic oligopeptides adopt an essentially unordered conformation in aqueous solution. 2-Chloroethanol supports in various amounts the onset of the right-handed alpha-helical form in the carboxy-peptidase fragments.

Secondary structure prediction of fish protamines

The secondary structures of thirteen fish protamines have been predicted by the statistical method of Chou and Fasman as well as by two modifications of it. The occurrence of phosphorylatable residues in predicted beta-turns is discussed. The results are compared with available spectroscopic observations.