# Conformational Analysis of Cyclolinopeptide A, a Cyclic Nonapeptide: Nuclear Overhauser Effect and Energy Minimization Studies

Raghothama, S and Ramakrishnan, C and Balasubramanian, D and Balaram, P (1989) Conformational Analysis of Cyclolinopeptide A, a Cyclic Nonapeptide: Nuclear Overhauser Effect and Energy Minimization Studies. In: Biopolymers, 28 . pp. 573-588.

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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 'H-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 NO& and JHNCaH values pennit 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(l)-Pro(P), with a cis peptide bond between these residues and a \gamma-turn ($C_7$ structure) centered at 1146). Two intramolecular hydrogen bonds Val(9) CO-Phe(3)NH (4 \rightarrow 1) and Leu(5) CO-Ile(7)NH (3 \rightarrow 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.