title: Crystal structure of a partly self-complementary peptide nucleic acid (PNA) oligomer showing a duplex-triplex network.
abstract: The X-ray structure of a partly self-complementary peptide nucleic acid (PNA) decamer (H-GTAGATCACT-l-Lys-NH(2)) to 2.60 A resolution is reported. The structure is mainly controlled by the canonical Watson-Crick base pairs formed by the self-complementary stretch of four bases in the middle of the decamer (G(4)A(5)T(6)C(7)). One right- and one left-handed Watson-Crick duplex are formed. The two PNA units C(9)T(10) change helical handedness, so that each PNA strand contains both a right- and a left-handed section. The changed handedness in C(9)T(10) allows formation of Hoogsteen hydrogen bonding between C(9)T(10) and G(4)A(5) of a PNA strand in an adjacent Watson-Crick double helix of the same handedness. Thereby, a PNA-PNA-PNA triplex is formed. The PNA unit A(3) forms a noncanonical base pair with A(8) in a symmetry-related strand of opposite handedness; the base pair is of the A-A reverse Hoogsteen type. The structural diversity of this PNA demonstrates how the PNA backbone is able to adapt to structures governed by the stacking and hydrogen-bonding interactions between the nucleobases. The crystal structure further shows how PNA oligomers containing limited sequence complementarity may form complex hydrogen-bonding networks.
authors.affiliation: Biostructural Research, Department of Medicinal Chemistry, The Danish University of Pharmaceutical Sciences, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
authors.forename: Britt
authors.initials: B
authors.lastname: Petersson
authors.forename: Bettina Bryde
authors.initials: BB
authors.lastname: Nielsen
authors.forename: Hanne
authors.initials: H
authors.lastname: Rasmussen
authors.forename: Ingrid Kjøller
authors.initials: IK
authors.lastname: Larsen
authors.forename: Michael
authors.initials: M
authors.lastname: Gajhede
authors.forename: Peter E
authors.initials: PE
authors.lastname: Nielsen
authors.forename: Jette Sandholm
authors.initials: JS
authors.lastname: Kastrup
mesh_terms: D020029:Base Pairing; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008958:Models, Molecular; D020135:Peptide Nucleic Acids / Q000737:chemistry*
chemical_list: D020135:Peptide Nucleic Acids