title: SPKK, a new nucleic acid-binding unit of protein found in histone.
abstract: A new DNA-binding unit of a protein different from the alpha-helix, the beta-sheet and the Zn-finger is proposed based on the analysis of the structure of the N-terminus of sea urchin spermatogenous histone H1. DNA-binding arms of the sea urchin spermatogenous histones, H1 and H2B, are composed of repeats of Ser-Pro-Lys(Arg)-Lys(Arg) (SPKK) residues. A six-times repeat of SPKK (S6 peptide) was isolated from H1 and the competition of S6 for DNA binding with a DNA-binding dye, Hoechst 33258, was analysed. The S6 peptide is shown to be a competitive inhibitor of Hoechst 33258, and it is concluded that the SPKK repeat binds to DNA in its minor groove with a binding constant, KS6 = 1.67 X 10(10) M-1. The circular dichroism (CD) spectrum of a synthetic peptide, SPRKSPRK (S2 peptide), is quite different from those of both the alpha-helix and the beta-sheet and resembles that of a random coil. From statistical consideration of protein structures it is proposed that SPKK forms a compact beta-turn stabilized by an additional hydrogen bond. Since a repeated chain of such turn of SPKK offers a repeat of amides of Ser residues at a distance similar to that of DNA-binding amides of the drugs, Hoechst 33258 and netropsin, and since the amides of these drugs bind to DNA replacing the spine of hydration in a minor groove, it is proposed that a repeat of SPKK binds to DNA in the minor groove using similar hydrogen bonds.
authors: Laboratory of Neurochemistry, National Institute for Physiological Sciences, Okazaki, Japan.
authors: M
authors: M
authors: Suzuki
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D006690:Bisbenzimidazole / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006657:Histones / Q000378:metabolism*; D008297:Male; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000378:metabolism*; D011487:Protein Conformation; D012617:Sea Urchins / Q000378:metabolism; D013094:Spermatozoa / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D006657:Histones; D009842:Oligopeptides; C059837:seryl-prolyl-lysyl-lysine; D006690:Bisbenzimidazole