title: Modelling and refinement of the crystal structure of nucleoprotamine from Gibbula divaricata.
abstract: The molecular structure of nucleoprotamine from Gibbula divaricata and its packing in oriented fibers has been modelled both to fit the X-ray diffraction pattern and to avoid steric compression. The representative model consists of 51 poly (dinucleotide) B-DNA helices with 51 poly(hexapeptide) chains associated with the major grooves. The prevailing peptide conformation is beta. The four arginine residues present are hydrogen-bonded to DNA phosphates while neutral peptides protrude into the minor grooves of neighboring nucleoprotamine molecules which are packed 2.61 nm apart in a screw-disordered, quasi-hexagonal lattice. This model reconciles a number of earlier, apparently conflicting experimental results and explains the remarkable stability of nucleoprotamines.
authors.affiliation: Unidad de Química Macromolecular del C.S.I.C., Escuela Técnica Superior de Ingenieros Industriales, Diagonal, Barcelona, Spain.
authors.forename: L C
authors.initials: LC
authors.lastname: Puigjaner
authors.forename: I
authors.initials: I
authors.lastname: Fita
authors.forename: S
authors.initials: S
authors.lastname: Arnott
authors.forename: R
authors.initials: R
authors.lastname: Chandrasekaran
authors.forename: J A
authors.initials: JA
authors.lastname: Subirana
mesh_terms: D000818:Animals; D004247:DNA; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D011479:Protamines / Q000648:ultrastructure*; D011487:Protein Conformation; D012908:Snails; D014961:X-Ray Diffraction
chemical_list: D011479:Protamines; C015786:deoxyribonucleoprotamine; D004247:DNA