The structure and biological characteristics of the Spirochaeta aurantia outer membrane glycolipid LGLB

Abstract

In an attempt to isolate lipopolysaccharide from Spirochaeta aurantia, Darveau-Hancock extraction of the cell mass was performed. While no lipopolysaccharide was found, two carbohydrate-containing compounds were detected. They were resolved by size-exclusion chromatography into high molecular mass (LGLA) and low molecular mass (LGLB) fractions. Here we present the results of the analysis of the glycolipid LGLB. Deacylation of LGLB with hydrazine and separation of the products by using anion-exchange chromatography gave two major products. Their structure was determined by using chemical methods, NMR and mass spectrometry. All monosaccharides had the D-configuration, and aspartic acid had the L-configuration. Intact LGLB contained two fatty groups at O-2 and O-3 of the glycerol residue. Nonhydroxylated C14 to C18 fatty acids were identified, which were predominantly unsaturated or branched. LGLB was able to gel Limulus amebocyte lysate, albeit at a lower level than that observed for Escherichia coli O113 lipopolysaccharide. However, even large amounts of LGLB were unable to stimulate any Toll-like receptor (TLR) examined, including TLR4 and TLR2, previously shown to be sensitive to lipopolysaccharide and glycolipids from diverse bacterial origins, including other spirochetes.