Synthesis, purification, NMR characterization and interaction with nucleotides of a fragement of a human protamine.

The peptide Arg-Arg-Ser-Ser-Ser-Arg-Pro-Ile-Arg-Arg (peptide I), which is a common fragment in many fish protamines, was previously suggested to promote strong purine nucleotide binding in these proteins. To verify this hypothesis, peptide I was synthesized by the solid-phase technique and purified by cation-exchange chromatog. The peptide was characterized by mono- and bi-dimensional NMR spectroscopy. NMR resonances were fully assigned both in the proton- and in the 13C-aliph. regions of the spectra. The interactions of the peptide with purine and pyrimidine mononucleotides in aq. solns. have been studied as a function of nucleotide concn. The addn. of pyrimidine nucleotides did not produce any relevant effect in the NMR spectrum. The presence of a purine nucleotide, on the contrary, produced remarkable upfield chem. shifts and a strong broadening of the peptide resonances. In the case of 5'-dGMP this broadening was accompanied by a very large redn. of the area of the peptide resonances. These results complement the behavior of fish protamines previously tested contg. the peptide I sequence, and fully support the original hypothesis.