Open AccessOsmoregulated periplasmic glucans of the free‐living photosynthetic bacterium Rhodobacter sphaeroides
Author(s) -
Talaga Philippe,
Cogez Virginie,
Wieruszeski JeanMichel,
Stahl Bernd,
Lemoine Jérôme,
Lippens Guy,
Bohin JeanPierre
Publication year - 2002
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1033.2002.02906.x
Subject(s) - chemistry , glycosidic bond , rhodobacter sphaeroides , glucan , periplasmic space , biochemistry , chromatography , stereochemistry , escherichia coli , photosynthesis , gene , enzyme
The osmoregulated periplasmic glucans (OPGs) produced by Rhodobacter sphaeroides , a free‐living organism, were isolated by trichloracetic acid treatment and gel permeation chromatography. Compounds obtained were characterized by compositional analysis, matrix‐assisted laser desorption ionization mass spectrometry and nuclear magnetic resonance. R. sphaeroides predominantly synthesizes a cyclic glucan containing 18 glucose residues that can be substituted by one to seven succinyl esters residues at the C 6 position of some of the glucose residues, and by one or two acetyl residues. The glucans were subjected to a mild alkaline treatment in order to remove the succinyl and acetyl substituents, analyzed by MALDI mass spectrometry and purified by high‐performance anion‐exchange chromatography. Methylation analysis revealed that this glucan is linked by 17 1,2 glycosidic bonds and one 1,6 glycosidic bond. Homonuclear and 1 H/ 13 C heteronuclear NMR experiments revealed the presence of a single α‐1,6 glycosidic linkage, whereas all other glucose residues are β‐1,2 linked. The different anomeric proton signals allowed a complete sequence‐specific assignment of the glucan. The structural characteristics of this glucan are very similar to the previously described OPGs of Ralstonia solanacearum and Xanthomonas campestris , except for its different size and the presence of substituents. Therefore, similar OPGs are synthesized by phytopathogenic as well as free‐living bacteria, suggesting these compounds are intrinsic components of the Gram‐negative bacterial envelope.