title: Conformational analysis of cyclolinopeptide A, a cyclic nonapeptide: nuclear Overhauser effect and energy minimization studies.
abstract: The conformation of cyclolinopeptide A [cyclo(Pro-Pro-Phe-Phe-Leu-Ile-Ile-Leu-Val)], a naturally occurring cyclic nonapeptide has been investigated in dimethylsulfoxide solution by 270 MHz 1H-nmr. A complete assignment of all C alpha H and NH resonances has been accomplished using two-dimensional correlated spectroscopy and nuclear Overhauser effects (NOEs). Analysis of interresidue NOEs and JHNC alpha H values permit construction of a molecular model for the cyclic peptide backbone. The crude model derived from nmr has been used as a starting point for energy minimization, which yields a refined structure largely compatible with nmr observations. The major features of the conformation of cyclolinopeptide A are a Type VI beta-turn centered at Pro(1)-Pro(2), with a cis peptide bond between these residues and a gamma-turn (C7 structure) centered at Ile(6). Two intramolecular hydrogen bonds Val(9) CO--Phe(3)NH (4----1) and Leu(5) CO--Ile(7)NH (3----1) are observed in the low-energy conformation. The limited solvent accessibility observed for the Val(9) and Leu(5) NH groups in the nmr studies are rationalized in terms of steric shielding.
authors.forename: S
authors.initials: S
authors.lastname: Raghothama
authors.forename: C
authors.initials: C
authors.lastname: Ramakrishnan
authors.forename: D
authors.initials: D
authors.lastname: Balasubramanian
authors.forename: P
authors.initials: P
authors.lastname: Balaram
mesh_terms: D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D010456:Peptides, Cyclic; D011487:Protein Conformation
chemical_list: D010456:Peptides, Cyclic; C055018:cyclolinopeptide A