title: Sequence-specific unusual (1-->2)-type helical turns in alpha/beta-hybrid peptides.
abstract: This article describes novel conformationally ordered alpha/beta-hybrid peptides consisting of repeating l-proline-anthranilic acid building blocks. These oligomers adopt a compact, right-handed helical architecture determined by the intrinsic conformational preferences of the individual amino acid residues. The striking feature of these oligomers is their ability to display an unusual periodic pseudo beta-turn network of nine-membered hydrogen-bonded rings formed in the forward direction of the sequence by 1-->2 amino acid interactions both in solid-state and in solution. Conformational investigations of several of these oligomers by single-crystal X-ray diffraction, solution-state NMR, and ab initio MO theory suggest that the characteristic steric and dihedral angle restraints exerted by proline are essential for stabilizing the unusual pseudo beta-turn network found in these oligomers. Replacing proline by the conformationally flexible analogue alanine (Ala) or by the conformationally more constrained alpha-amino isobutyric acid (Aib) had an adverse effect on the stabilization of this structural architecture. These findings increase the potential to design novel secondary structure elements profiting from the steric and dihedral angle constraints of the amino acid constituents and help to augment the conformational space available for synthetic oligomer design with diverse backbone structures.
authors.affiliation: Division of Organic Chemistry, Center for Materials Characterization, Central NMR Facility, National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411 008, India.
authors.forename: Panchami
authors.initials: P
authors.lastname: Prabhakaran
authors.forename: Sangram S
authors.initials: SS
authors.lastname: Kale
authors.forename: Vedavati G
authors.initials: VG
authors.lastname: Puranik
authors.forename: P R
authors.initials: PR
authors.lastname: Rajamohanan
authors.forename: Olga
authors.initials: O
authors.lastname: Chetina
authors.forename: Judith A K
authors.initials: JA
authors.lastname: Howard
authors.forename: Hans-Jörg
authors.initials: HJ
authors.lastname: Hofmann
authors.forename: Gangadhar J
authors.initials: GJ
authors.lastname: Sanjayan
mesh_terms: D000409:Alanine / Q000737:chemistry; D000595:Amino Acid Sequence; D000621:Aminoisobutyric Acids / Q000737:chemistry; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000737:chemistry*; D011392:Proline / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D062367:ortho-Aminobenzoates / Q000737:chemistry*
chemical_list: D000621:Aminoisobutyric Acids; D010455:Peptides; D062367:ortho-Aminobenzoates; C100049:2-aminoisobutyric acid; D011392:Proline; D000409:Alanine