Structural elucidation of the biological repeating unit of O-specific polysaccharide from Citrobacter serotype O41.

Sugar analysis of the O-specific polysaccharide produced by Citrobacter serotype O41 revealed the presence of a hexasaccharide repeating unit, which includes the unusual 3-amino-N-(D-3'-hydroxybutyryl)-3,6-dideoxy-D-galactosyl residue (Fuc3NAcyl). The structure of the repeating unit was determined by extensive use of homo- and heteronuclear two-dimensional NMR spectroscopy, including the application of long-range 1H-13C correlation experiments and NOE studies to establish the sequence of sugar units. Indentification of the Glc beta 1-->2Fuc3NAcyl beta 1-->6GlcNAc alpha 1-->sequence at the non-reducing terminus establishes the biological repeating unit of this O-specific polysaccharide as: -->2Glc beta 1-->Fuc3NAcyl-beta 1-->6GlcNAc alpha 1-->(Glc alpha 1-->2) 4Gal beta 1-->3GalNAc beta 1-->. This structure is similar to that found for the O-specific polysaccharide isolated from Hafnia alvei strain 1211 [Katzenellenbogen, E., Romanowska, E., Dabrowski, U. & Dabrowski, J. (1991) Eur. J. Biochem. 200, 401-407], which differs in having an acetyl substituent at O4 of the Fuc3NAcyl residue and a branch point of GalNAc alpha substituted by Glc beta at O3; these differences are responsible for the only weak serological cross-reactivity of the two strains.