Biosynthesis of the 09 antigen of Escherichia coli. Core structure of rfe mutant as indication of assembly mechanism

The chemical structure of the outer (hexose) regions of the core oligosaccharide from Escherichia coli 09 with the complete R1 core, and from a R1-derived rfe mutant were analyzed using compositional analysis, methylation and gas chromatography/mass spectrometry. It was found that, in contrast to the branched outer region of the R1 core, the outer region of the core from the rfe mutant lacked terminal glucose and was linear. These results are in agreement with recent findings on the biosynthesis of the 09 antigen. They suggest a cotransfer of glucose with the 09-specific mannan to a 'pre-core' lacking terminal glucose, as the assembly (translocation) step in the 09 antigen synthesis. Thus it is suggested that the initiation of O-chain synthesis (by the formation of an acceptor glucolipid ) and the termination of core synthesis are closely correlated. In conjunction with previous biochemical data, the analytical results presented here indicate a novel core synthesis.