title: Structural elucidation of the outer core tetrasaccharide isolated from the LPS of Rhizobium leguminosarum bv. trifolii strain 24.
abstract: The outer core oligosaccharide (OS) was isolated from the lipopolysaccharide (LPS) of Rhizobium leguminosarum bv. trifolii strain 24 after Smith degradation and then studied by sugar and methylation analyses along with NMR and mass spectrometry methods. Negative-ion electrospray (ESI-MS) mass spectrum showed two molecular ions at m/z 686.3 and 728.3, which corresponded to the core OS having the composition Rha2QuiNAcKdh. The mass difference between both ions indicated that the higher molecule mass represented the mono O-acetylated variant of the OS. The sequence of the oligosaccharide was reflected in CID MS/MS spectra. In turn, NMR spectroscopy confirmed the composition and glycosylation pattern of the core OS and provided additional evidence on its structure. 2D NMR experiments revealed that the terminal Rhap is acetylated at position O-2. Moreover, 3-deoxyheptulosonic acid (Kdh), which was detected at the reducing terminus of the OS, was evidently derived from the Kdo as a result of Smith degradation. In addition, the higher intensity of signals for a six-membered pyranose ring of Kdhp over 2,7-anh-Kdhf seemed to indicate prevalence of this form of the sugar in the OS-derived species. Based on the data obtained, the following structure of the outer core tetrasaccharide, which probably links the O-chain polysaccharide to the inner core in the LPS of R. leguminosarum bv. trifolii strain 24, was established: α-L-Rhap-2-OAc*-(1-->3)-α-L-Rhap-(1-->3)-β-D-QuipNAc-(1-->4)-Kdo * ~ 50%. .
authors.affiliation: Department of Genetics and Microbiology, M. Curie-Sklodowska University, 19, Akademicka St., 20-033 Lublin, Poland. Electronic address: aturska@hektor.umcs.lublin.pl.
authors.forename: Anna
authors.initials: A
authors.lastname: Turska-Szewczuk
authors.affiliation: Department of Genetics and Microbiology, M. Curie-Sklodowska University, 19, Akademicka St., 20-033 Lublin, Poland.
authors.forename: Ryszard
authors.initials: R
authors.lastname: Russa
authors.affiliation: Department of Genetics and Microbiology, M. Curie-Sklodowska University, 19, Akademicka St., 20-033 Lublin, Poland.
authors.forename: Magdalena A
authors.initials: MA
authors.lastname: Karaś
authors.affiliation: Institute of Organic Chemistry, Polish Academy of Sciences, 44/52, Kasprzaka St., 01-224 Warsaw, Poland.
authors.forename: Witold
authors.initials: W
authors.lastname: Danikiewicz
authors.affiliation: Institute of Organic Chemistry, Polish Academy of Sciences, 44/52, Kasprzaka St., 01-224 Warsaw, Poland.
authors.forename: Grzegorz
authors.initials: G
authors.lastname: Spólnik
mesh_terms: D002240:Carbohydrate Sequence; D008070:Lipopolysaccharides / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D009844:Oligosaccharides / Q000737:chemistry*; D016961:Rhizobium leguminosarum / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry
chemical_list: D008070:Lipopolysaccharides; D009844:Oligosaccharides
keywords: Kdo; Lipopolysaccharide; Outer core oligosaccharide; QuiNAc; Rha; Rhizobium leguminosarum