Structures of the antigenic O-polysaccharides of lipopolysaccharides produced by Actinobacillus actinomycetemcomitans serotypes a, c, d and e.
Actinobacillus actinomycetemcomitans is a gram-negative capnophilic coccobacillus that has been implicated in the etiology of certain forms of early-onset periodontitis as well as non-oral infections, mostly bacterial endocarditis.  Five distinct serotypes of A. actinomycetemcomitans have been described.  Although the O-polysaccharide (O-PS) of lipopolysaccharide (LPS) has been shown to define the serologic specificity for this species, only the structure of the O-PS of serotype b has been characterized.  The focus of the current study was to define the structures of the O-PS of A. actinomycetemcomitans serotypes a, c, d and e. Structure determination was accomplished through the use of methylation, periodate oxidation, and one-dimensional and two-dimensional NMR methods.  The O-PS of A. actinomycetemcomitans (OMZ-542) serotype d had [alpha]D +15 degrees and was composed of D-glucose, D-mannose and L-rhamnose (L-Rha) in a molar ratio of 1:2:1.  Methylation, periodate oxidation, and two-dimensional 1H-NMR and 13C-NMR studies showed that the antigenic O-PS was a high-molecular-mass polymer composed of repeating tetrasaccharide units with the structure: [formula: see text] The O-PS of the LPS produced by A. actinomycetemcomitans (ATCC 29523) serotype a had [alpha]D +150 degrees and was found to contain 6-deoxy-D-talose (6dTalp) and O-acetyl (2:1) and was a high-molecular-mass polymer composed of O-acetyl-substituted repeating disaccharide units with the structure: [formula: see text] The O-PS of the LPS of A. actinomycetemcomitans (SUNY 67) serotype c had [alpha]D -170 degrees and was composed of 6-deoxy-L-talose and O-acetyl (2:1).  Structural analysis showed that the O-PS was a high-molecular-mass polymer of repeating disaccharide units with the structure: [formula: see text] The O-PS of the LPS of A. actinomycetemcomitans (OMZ 534) serotype e had [alpha]D +57 degrees and was composed of 2-acetamido-2-deoxy-D-glucose and L-rhamnose (1:1) and by chemical and NMR analysis was found to be a polymer of repeating disaccharide units with the structure: -->4)-alpha-D-GlcpNAc-(1-->3)-alpha-L-Rhap-(1-->.