Structural studies on the acidic exopolysaccharide from Haloferax denitrifricans ATCC 35960

The structure of a linear, acidic exopolysaccharide isolated from the Archa eon Haloferax denitrificans ATCC 35960 has been determined using NMR spectr oscopy. The sugar residues in the repeating unit of the polysaccharide were identified as Gal and GlcA2,3NAc after the assignment of the H-1 and C-13 resonances using COSY, HOHAHA, HMQC and HMQC-TOCSY experiments. The sequenc e of the residues in the polysaccharide was established from the inter-resi due connectivities observed in the HMQC-NOESY plot. The only sugar released on acid hydrolysis was shown to be D-Gal by GLC analysis, while the absolu te configuration of the acidic sugars was shown to be D by comparison of th e carbon chemical shifts with those of model compounds. Partial acid hydrol ysis yielded a tetrasaccharide, terminated by D-Gal at the reducing end, wh ose structure confirmed that of the repeating unit of the polysaccharide as --> 4)-beta-D-GlcpA2,3NAc-(1 --> 4)-beta-D-GlcpA2,3NAc-(1 --> 4)-alpha-D-G lcpA2,3NAc-(1 --> 3)-alpha-D-Galp-(1 -->, where D-GlcpA2,3NAc is 2,3-diacet amido-2,3-dideoxy-D-glucopyranosiduronic acid. (C) 1999 Elsevier Science Lt d. All rights reserved.