title: A nonhelical, multiple beta-turn conformation in a glycine-rich heptapeptide fragment of trichogin A IV containing a single central alpha-aminoisobutyric acid residue.
abstract: The conformational properties of the protected seven-residue C-terminal fragment of the lipopeptaibol antibiotic Trichogin A IV (Boc-Gly-Gly-Leu-Aib-Gly-Ile-Leu-OMe) has been examined in CDCl3 and (CD3)2SO by 1H-nmr. Evidence for a multiple beta-turn conformation [type I' at Gly(1)-Gly(2), type II at Leu(3)-Aib(4), and a type I' at Aib(4)-Gly(5)] suggests that Leu(3) has preferred an extended or semiextended conformation over a helical conformation in CDCl3. This structure is thus in contrast to earlier observations of seven-residue peptides containing a single central Aib preferring helical conformations in both solution and crystalline states. A structural transition to a frayed right-handed helix is observed in (CD3)2SO. These results suggest that nonhelical conformations may be important in Gly-rich peptides containing Aib. Further, the presence of amino acids with contradictory influences on backbone conformational freedom can lead to well-defined conformational transitions even in small peptides.
authors.affiliation: Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India.
authors.forename: R
authors.initials: R
authors.lastname: Gurunath
authors.forename: P
authors.initials: P
authors.lastname: Balaram
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000737:chemistry*; D002942:Circular Dichroism; D003196:Computer Graphics; D005998:Glycine; D055666:Lipopeptides; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000737:chemistry* / Q000302:isolation & purification; D010455:Peptides; D017433:Protein Structure, Secondary; D013816:Thermodynamics
chemical_list: D000900:Anti-Bacterial Agents; D055666:Lipopeptides; D010446:Peptide Fragments; D010455:Peptides; C087937:trichogin A IV; D005998:Glycine