Calculations of the Conformations of Iturin A in Relation with NMR Studies

Abstract

Iturin A is an antifungal antibiotic which was isolated from a strain of Bacillus subtilis, and contains a lipophilic β amino acid closing an heptapeptide cycle with polar L and D residues. Iturin A belongs to a lipopeptide family of which the LDDLLDL sequence is kept constant.

NMR spectroscopy and semi-empirical energy calculations are combined to design the conformations of Iturin A in pyridine solution. J coupling constants and nOes (nuclear Overhauser enhancements) are used as guiding line for energy calculations. This preliminary study shows that Iturin A in pyridine appears as rather rigid, especially in the L Pro 5—D Asn 6 region, probably involved in a β turn. The polar side chains can form different networks of intramolecular hydrogen bonds. The Tyr side chain, relatively mobile, could be involved in interactions with an hydrophobic environment as the β amino acid side chain found away from the peptide cycle.