Confirmation of the anomeric structure of galacturonic acid in the galacturonosyl-ceramide of Sphingomonas yanoikuyae

The anomeric structure of glycosphingolipids significantly influences their activity to stimulate natural killer T cells. In this study the chemical structure of the galacturonosyl-ceramide in Sphingomonas yanoikuyae, designated GSL-1'sy, was re-examined to prove the anomeric structure of the Dgalacturonic acid (GalA) in the lipid, which was reported as beta-configuration by Naka et al., but was suggested as alpha-configuration in our preliminary study. GSL-1'sy was purified from the bacterial cells with the same procedure as Naka et al. The 1H-NMR analysis of GSL-1'sy revealed that the coupling constant of the anomeric proton of GalA was 3.0 Hz, indicating that GalA in GSL-1'sy is alpha-anomer, the configuration active for the stimulation of natural killer T cells.