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At least 55 records · Page 3Linked to original sources
PubMed1991

Nature of protamine-DNA complexes. A special type of ligand binding co-operativity.

The mode of protamine binding to DNA double helices has been analyzed for the example of clupein Z from herring and DNA samples from bacteriophages lambda and PM2 by measurements of light-scattering intensities, ultracentrifugation and kinetics. The light-scattering intensity of DNA increases co-operatively at a threshold clupein concentration suggesting co-operative binding of clupein to double helices. These data are first analyzed in terms of a model with a transition at a threshold degree of binding. The parameters resulting from this analysis appear to be reasonable, but are shown to be in contrast with data on the absolute degree of clupein binding to DNA obtained by centrifugation experiments. An analysis of the kinetics associated with clupein binding to DNA by measurements of the time-dependence of light-scattering intensities in the time range of seconds demonstrates directly that clupein-induced intermolecular interactions of DNA molecules are essential. The rate constants of DNA association increase co-operatively at threshold clupein concentrations, which correspond to those observed in the equilibrium titrations. Above the threshold, the rate constants arrive at a level that is almost constant, but shows some decrease with increasing clupein concentrations. These results are described by a model with a monomer and a dimer state of DNA, which bind ligands with different affinities according to an excluded-site binding scheme. When the ligand binding constant is larger for the dimer than for the monomer state, as should be expected, binding of ligands drives the DNA from the monomer to the dimer state, even if the dimerization equilibrium in the absence of ligands is far in favor of the monomer. The transition from the monomer to the dimer state proves to be strongly co-operative. When the ligand concentration is increased to higher values, the dimers may be converted back to monomers due to an increased extent of ligand binding to the monomer state. The model is consistent with the available experimental data. The analysis of the data by the model indicates the existence of a reaction unit much below the DNA chain length, corresponding to about 80 nucleotide residues. The present model describes ligand driven intermolecular association; an analogous model is applicable to ligand driven intramolecular association. In summary, the co-operativity of clupein binding to DNA double helices is not due to nearest neighbor interactions, but results from thermodynamic coupling of clupein binding with clupein-induced DNA association.

Bacteriophages↗
PubMed1989

Complex dielectric constant of arginine-DNA and protamine-DNA aqueous systems at 10 GHz.

The complex dielectric constant of arginine and protamine from herring sperm (clupeine) and their complexes with herring sperm DNA was measured at 10 GHz in the temperature range -20 to +45 degrees C by a microwave cavity perturbation method. The experimental results were analysed in terms of a three-component equation (solute molecules, interfacial water and bulk water) to calculate the fractional volume of modified water and hence the specific hydration of the samples. A fourfold reduction of the specific hydration is observed for the clupeine molecule as compared to the free monomers. This is consistent with a folded conformation of the protein in solution. The specific hydration of the complex between clupeine and DNA is reduced by 50% with respect to the weighted average for the uncomplexed components. This result indicates an intimate contact between clupeine and DNA with exclusion of water molecules and is consistent with the highly condensed form of nucleoprotamines which is known in vivo.

Animals↗
PubMed1975

Chemical synthesis of partially and fully phosphorylated protamines.

Chromatographically purified components Z and YI of clupeine from herring have been phosphorylated by a chemical method. To enhance solubility in trimethylphosphate, the protamine capronate salts were used and phosphorylation was performed with POCl3. Both serine and threonine residues were phosphorylated; however, besides monophosphate esters considerable amounts of polyphosphate esters were obtained. Its nature was identified by 31P nuclear magnetic resonance spectroscopy and by chemical methods, such as comparison of the hydrolysis rate with that of ADP and phoshocreatine, respectively. The pyrophosphate bonds were cleaved by controlled hydrolysis with HCl. The phosphorylated protamine species were purified by gel filtration and chromatography on a Sephadex CM column. Fully phosphorylated clupeine Z (3 serine residues and 3 phosphates) and YI (3 serine, 2 threonine residues and 5 phosphates) were obtained as well as partially phosphorylated fractions; in the case of clupeine Z the resolution into mono, doubly and triply (fully) phosphorylated fractions was excellent. The overall yield of phosphorylated clupeine was better than 50%.

Amino Acids↗
PubMed1988

Comparison of phosphorylation sites in protamines between protein kinase C and cAMP-dependent protein kinase.

Phosphorylation sites of protamines by protein kinase C and cAMP-dependent protein kinase (protein kinase A) were studied. Using clupeine Y1 as a substrate, protein kinase C phosphorylates both Ser and Thr residues, whereas protein kinase A phosphorylates only Ser residue(s). Protein kinase C phosphorylates all Ser and Thr residues of clupeine Y2 and Z, however protein kinase A phosphorylates mainly Ser9 and slightly Thr5 in clupeine Y2 and Ser6 and Ser10 in clupeine Z. These results suggest that protein kinase C recognizes more sites than those of protein kinase A and may participate in protamine phosphorylation in vivo.

Amino Acid Sequence↗