The importance of the outer membrane and of its main constituent, lipopolysaccharide, in the symbiosis between rhizobia and leguminous host plants has been well studied. Here, the first complete structural characterization of the entire lipopolysaccharide from an O-chain-deficient Bradyrhizobium ORS285 rfaL mutant is achieved by a combination of chemical analysis, NMR spectroscopy, MALDI MS and MS/MS. The lipidA structure is shown to be consistent with previously reported Bradyrhizobium lipidA, that is, a heterogeneous blend of penta- to hepta-acylated species carrying a nonstoichiometric hopanoid unit and possessing very-long-chain fatty acids ranging from 26:0(25-OH) to 32:0(31-OH). The structure of the core oligosaccharide region, fully characterized for the first time here, is revealed to be a nonphosphorylated linear chain with methylated sugar residues, with a heptose residue exclusively present in the outer core region, and with the presence of two singly substituted 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) residues, one of which is located in the outer core region. The lipidA moiety is linked to the core moiety through an uncommon 4-substituted Kdo unit.
NMR spectroscopy, symbiosis, mass spectrometry, lipooligosaccharides, bradyrhizobium ORS285
NCBI PubMed ID: 28794950Publication DOI: 10.1002/open.201700074Journal NLM ID: 101594811Publisher: Weinheim: Wiley-VCH
Correspondence: Silipo A
Institutions: Department of Chemical Sciences, University of Naples Federico II, via Cinthia 4, 80126, Naples, Italy, IRD, Laboratoire des Symbioses Tropicales et Mediterraneennes, UMR IRD/SupAgro/INRA/UM2/CIRAD, Campus International de Baillarguet, TA A-82/J, 34398, Montpellier Cedex 5, France, CNR-Istituto per i Polimeri, Compositi e Biomateriali IPCB—Unità di Catania, Via Gaifami 18, 95126, Catania, Italy, Junior Group of Allergobiochemistry, Research Center Borstel, Leibniz Center for Medicine and Biosciences, Airway Research Center North (ARCN), German Center for Lung Research, Borstel, Germany
Methods: 13C NMR, 1H NMR, methylation, GLC-MS, NMR-2D, SDS-PAGE, acid hydrolysis, MALDI-TOF MS, composition analysis, methanolysis, GPC, HPAEC-PAD, reduction with NaBD4, acetylation, MALDI-TOF/TOF MS
Found