The relative orientation of the lipid and carbohydrate moieties of lipochitooligosaccharides related to nodulation factors depends on lipid chain saturation

Abstract

Lipochitooligosaccharides (LCOs) signal the symbiosis of rhizobia with legumes and the formation of nitrogen-fixing root nodules. 1 and 2 share identical tetrasaccharide scaffolds but different lipid moieties (1, LCO-IV(C16:1[9Z], SNa) and 2, LCO-IV(C16:2[2E,9Z], SNa)). The conformational behaviors of both were studied by molecular modeling and NMR. Modeling predicts that a small lipid modification would result in a different relative orientation of the lipid and tetrasaccharide moieties. Diffusion ordered spectroscopy reports that both form small aggregates above 1 mM. Nuclear Overhauser spectroscopy (NOESY) data, collected under monomeric conditions, reveals lipid–carbohydrate contacts only for 1, in agreement with the modeling data. The distinct molecular structures of 1 and 2 have the potential to contribute to their selective binding by legume proteins.