title: Characterization of bent helical conformations in polymorphic forms of a designed 18-residue peptide containing a central Gly-Pro segment.
abstract: An 18-residue sequence Boc-Aib-Val-Ala-Leu-Aib-Val-Ala-Leu-Gly-Pro-Val-Ala-Leu-Aib-Val-Ala-Leu-Aib-OMe (UK18) was designed to examine the effect of introducing a Gly-Pro segment into the middle of a potentially helical peptide. The crystal structures of two polymorphic forms yielded a view of the conformation of three independent molecules. Form 1 (space group P2(1)2(1)2(1,) a = 14.620Å; b = 26.506Å, c = 28.858Å, Z = 4) has one molecule in the asymmetric unit, with one cocrystallized water molecule. Form 2 (space group P2(1)2(1)2(1,) a = 9.696Å; b = 19.641Å, c = 114.31Å, Z = 8) has two molecules in the asymmetric unit with four cocrystallized water molecules. In Form 1, residues 1 to 18 adopt ϕ,ψ values that lie in the right-handed helical (α(R) ) region of the Ramachandran map. Two residues, Leu (8) (ϕ = -92.0°, ψ = -7.5°) and Leu (17) (ϕ = -94.7°, ψ = -1.7°) adopt conformations that deviate significantly from helical values. In Form 2, molecule A, residues 2 to 16 lie in the α(R) region of ϕ,ψ space, with Leu (8) (ϕ = -94.9°, ψ = -2.9°) deviating significantly from helical values. Aib (1) and Aib (18) adopt left-handed (α(L)) helical conformation. Significant distortion is observed at Leu (17) (ϕ = -121.3°, ψ = -31.3°). Molecule B, Form 2, adopts a right-handed helix over residues 1 to 17. In all three molecules, a distinct bend in the helix is observed, with the bend angle values varying from 40.8° to 58.9°.
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore-560012, India.
authors.forename: Subrayashastry
authors.initials: S
authors.lastname: Aravinda
authors.forename: Narayanaswamy
authors.initials: N
authors.lastname: Shamala
authors.forename: Isabella L
authors.initials: IL
authors.lastname: Karle
authors.forename: Padmanabhan
authors.initials: P
authors.lastname: Balaram
mesh_terms: D000595:Amino Acid Sequence; D006860:Hydrogen Bonding; D009842:Oligopeptides / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D014867:Water
chemical_list: D009842:Oligopeptides; D010455:Peptides; D014867:Water